際に【さいに】

The expression 際に (さいに) means "when," "at the time of," or "on the occasion of." It is used to indicate a specific time or occasion when something happens or should happen. It is more formal than とき時に (ときに) and is commonly found in written language, announcements, instructions, official notices, and formal speech.

Structure

• Verb (dictionary form) + 際に: When doing something

  にっぽん日本にいく行くさいに際に、ぱすぽうとパスポートをわすれないで忘れないでください。

  When you go to Japan, please don't forget your passport.

• Verb (past form) + 際に: When (something happened)

  せんじつ先日おあいしたお会いしたさいに際に、めいし名刺をいただきました。

  When I met you the other day, I received your business card.

• Noun + の + 際に: At the time of (noun)

  おもうしこみ申し込みのさいに際に、みぶんしょうめいしょ身分証明書がひつよう必要です。

  An ID is required at the time of application.

Usage notes

際に is interchangeable with 際は in many cases. Using 際は emphasizes the condition ("if/when that situation arises"), while 際に focuses more on the specific moment.

Unlike the more casual とき時に, さいに際に carries a formal tone and is not typically used in everyday casual conversation. It is especially common in contexts like instructions, manuals, public announcements, and business communication.

With この/その/あの

際に can also be used with demonstratives to refer to a previously mentioned or upcoming occasion.