on the occasion of; when

際に marks a special occasion or moment when something is done, a formal equivalent of とき. Attach it to a verb's dictionary or past form, or a noun with の. It suits announcements, instructions, and polite speech.

Examples

• お降ふりの際さいは、足元あしもとにご注意ちゅういください。

  Oori no sai wa, ashimoto ni go-chuui kudasai.

  When getting off, please watch your step.

• 申もうし込こみの際さいに、身分証みぶんしょうが必要ひつようです。

  Moushikomi no sai ni, mibunshou ga hitsuyou desu.

  When you apply, you need an ID.

Vocabulary in these examples

• 注意 attention, caution
• くださる to give (honorific)
• 必要 necessary, necessity

Related patterns · Time and sequence

• 〜に先立って prior to; in advance of
• 〜て以来 ever since
• 〜次第 as soon as
• 〜たとたんに the moment that; just as
• 〜最中に in the middle of; right while