〜際に (さいに): 'On the Occasion Of' (Formal 'When')
What it means
際(さい) literally means "occasion" or "juncture," and 〜際に marks the moment or situation in which something is done. It maps onto English "when," "on the occasion of," or "at the time of."
The catch is register. While 〜とき is the neutral, all-purpose "when," 際に is formal and somewhat written. You hear it in station announcements, on printed notices, and in polite business situations — places 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.
Notice these all share a polite, public-facing tone. That is exactly where 際に lives.
How to form it
Attach 際に to a verb in plain form (dictionary or past た), or to a noun + の. The に can become は for contrast/topic, or drop entirely in 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) |
A nuance worth knowing: Vる + 際に points to before/as the action happens, while Vた + 際に points to after it has happened — the same dictionary-vs-た distinction you already use with とき.
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 vs とき vs 場合
These three all translate as "when / in case," but they differ:
- 〜とき — the neutral, everyday "when." Works in any register, casual or formal. If you are just talking, use とき.
- 〜際に — a formal, deliberate "when," for notices, announcements, and polite business. Same situations as とき, but dressed up.
- 〜場合(ばあい)は — "in the case that / if," emphasizing a hypothetical condition rather than a moment 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; the choice is about tone. 場合 leans more toward "if this situation arises."
Common mistakes
- Using 際に in casual speech. Telling a friend 駅に着いた際に電話して sounds stiff and odd — say 駅に着いたとき電話して instead. Reserve 際に for formal/written contexts.
- Forgetting の after a noun. It's 利用の際に, not 利用際に. Nouns always connect with の.
- Pairing it with trivial, everyday occasions. 際に suits weighty or deliberate occasions (joining, applying, an emergency, getting off a train). 歯を磨く際に ("when brushing my teeth") feels comically over-formal — use とき.
- Confusing it with 場合. 際に marks the time/occasion of an action; 場合 frames a condition ("in case"). Don't swap them when you mean a hypothetical.
Quick recap
- 〜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.
Your turn
Choose the correct use of 際に / の際に (and when とき fits better).
Start the 5-question drill →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, …').