〜際に (さいに): 'On the Occasion Of' (Formal 'When')
A "when" that wears a suit
際(さい) literally means "occasion" or "juncture," and 〜際に marks the moment or situation in which something is done — English "when," "on the occasion of," or "at the time of." In plain meaning it is nothing more than a "when."
What sets it apart is register. Where 〜とき is the neutral, all-purpose "when," 際に is formal and somewhat written — the language of station announcements, printed notices, and polite business, where the speaker is being deliberate and courteous about a particular occasion.
お降りの際は、足元にご注意ください。
おおりの さいは、あしもとに ごちゅうい ください。
When getting off, please watch your step.
Classic station / bus announcement phrasing.
ご利用の際は、会員証をご提示ください。
ごりようの さいは、かいいんしょうを ごていじ ください。
When using (the facility), please show your membership card.
入会の際に、書類が必要です。
にゅうかいの さいに、しょるいが ひつようです。
Documents are required at the time of joining.
Every one of these carries a polite, public-facing tone — the natural habitat of 際に.
Attaching it, and the する / した split
際に clips onto a verb in plain form (dictionary or past た), or onto a noun + の. The に can shift to は for contrast/topic, or drop entirely in signage and headings.
| Connects to | Pattern | Example |
|---|---|---|
| Verb (dictionary) | Vる + 際に | 申し込む際に (when applying) |
| Verb (past) | Vた + 際に | 来た際に (when [someone] came) |
| Noun | N + の + 際に | 緊急の際に (in an emergency) |
| Topic / contrast | 〜際は | お帰りの際は (when leaving) |
The tense in front still does the timing work: Vる + 際に points to before/as the action happens, while Vた + 際に points to after it is done — the same dictionary-vs-た distinction you already run with とき. And a noun always needs の to connect: 利用の際に, never 利用際に.
ヤッタンは図書館を利用する際に、学生証を見せた。
ヤッタンは としょかんを りようする さいに、がくせいしょうを みせた。
When using the library, Yattan showed his student ID.
Vる際に = at the point of doing the action.
先生は教室に入った際に、窓を開けてくださいました。
せんせいは きょうしつに はいった さいに、まどを あけて くださいました。
When the teacher entered the classroom, she opened the window for us.
Vた際に = after the action had taken place.
モチは引っ越しの際に、たくさんの本を処分した。
モチは ひっこしの さいに、たくさんの ほんを しょぶんした。
On the occasion of moving, Mochi got rid of a lot of books.
Noun + の + 際に.
際に, とき, or 場合?
All three surface in English as "when / in case," but they split along two axes — register and whether the clause is a moment or a condition:
- 〜とき — the neutral, everyday "when." Works in any register, casual or formal. If you are simply talking, reach for とき.
- 〜際に — a formal, deliberate "when," for notices, announcements, and polite business. The same situations as とき, only dressed up.
- 〜場合(ばあい)は — "in the case that / if," stressing a hypothetical condition rather than a point in time: 雨の場合は中止です ("In case of rain, it's cancelled").
So 際に and とき overlap in meaning and part ways on tone; 場合 is the odd one out, leaning toward "if this situation arises." Swapping 際に in for 場合 when you mean a hypothetical is the mistake to guard against.
When 際に turns comic
The formal robe misleads learners in two directions. Wear it too casually and it clangs: 駅に着いた際に電話して to a friend sounds stiff and strange — say 駅に着いたとき電話して. Wear it for something trivial and it turns absurd: 際に wants weighty, deliberate occasions (joining, applying, an emergency, getting off a train), so 歯を磨く際に ("when brushing my teeth") is comically over-formal — that is plain とき territory. Keep 際に for the public, ceremonious moments it was cut for.
The short version
- 〜際(さい)に = a formal "when" / on the occasion of.
- Form: Vる/Vた + 際に, or N + の + 際に; also 〜際は.
- Same meaning as とき, but for announcements, signs, and business — not casual talk.
- 場合は = "in case," stressing a hypothetical condition.
Practice it
Choose the correct use of 際に / の際に (and when とき fits better).
＿＿＿に入れるのに最もよいものを選びなさい。
電車をお降りの＿＿＿、足元にご注意ください。
Frequently asked questions
What's the difference between 際に and とき?
They mean the same thing — 'when' — but 際に is formal and written, used in announcements, signs, and polite business. とき is neutral and works everywhere, including casual conversation.
How does 際に connect to nouns and verbs?
Verbs take plain form: 利用する際に, 来た際に. Nouns need の: 入会の際に. You can also use 際は for topic or contrast.
Is there a difference between Vる際に and Vた際に?
Yes — like with とき, Vる際に refers to before/as the action happens, while Vた際に refers to after it has happened: 入る際に (as you enter) vs 入った際に (once you have entered).
When should I use 場合 instead of 際に?
Use 場合は for a hypothetical condition ('in case of rain, …'). Use 際に for the time or occasion of a real action ('when getting off, …').
Where 〜際に fits
Shaky on this? Get these solid first
- 〜とき · N5 — とき(時) means 'when' in Japanese: attach plain form + とき. Learn noun+の, な-adj+な, plain verbs, and the key 行くとき vs 行ったとき tense difference.
Don't confuse it with
- 〜うちに · N3 — 〜うちに means 'while a state lasts' — do something before it changes: 明るいうちに帰ろう. Learn 〜ないうちに ('before X happens'), 〜ているうちに, and うちに vs 間に.
More N3 grammar to explore
Keep going with related patterns at the same level:
- 〜とおり / 〜どおり — 〜とおり(に) and 〜どおり mean 'exactly as / in accordance with.' Learn verb + とおり, noun + のとおり, the voiced suffix どおり (予定どおり), and the dict-vs-た choice.
- 〜ついでに — 〜ついでに means doing a second thing while you're already doing the first: verb/noun + ついでに. Learn the formation, which action is the 'main' one, and common mistakes.
- つまり — つまり restates or sums up what you just said — 'in other words,' 'that is,' 'in short.' Learn how to use it, how it pairs with ということだ, and how it differs from すなわち and 要するに.
- 〜わけだ — 〜わけだ marks a logical conclusion that naturally follows from facts: 'so that means,' 'no wonder,' 'it follows that.' Learn the formation and how it differs from はず and から.
- 〜わけではない — 〜わけではない softly corrects an assumption: 'it's not that…' / 'it doesn't necessarily mean…'. Learn the formation, the casual わけじゃない, and how it differs from わけがない.
- 〜を中心に — 〜を中心に means 'centered on / mainly / with X at the center.' Learn the formation, the を中心として and を中心にして variants, and the adnominal を中心とした.