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JLPT N2ConstructionFormal
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際さい（に）When; on the occasion of

際さい formally marks the time or defined occasion when something happens. It is especially common in notices, procedures, business communication, and careful explanations.

A defined occasion

際さい treats a situation as a clearly identified occasion connected with an instruction, procedure, or other event. With に, it locates the following event in time. In instructions and contingencies, it often appears with は or には to present what should be done in that situation.

Notices and practical contingencies

This formal style is particularly natural when giving instructions that apply whenever a stated situation occurs.

館かん内ないを見けん学がくする際さいは、受うけ付つけで身み分ぶん証しょう明めい書しょをご提てい示じください。

When touring the building, please present identification at reception.

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機き器きに異い常じょうが発はっ生せいした際さいには、直ただちに電でん源げんを切きってください。

If an abnormality occurs in the equipment, turn off the power immediately.

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Although the verb before 際さい is in the past form, this is a contingency instruction, not a claim that the problem has already occurred.

Choosing the verb form

The nonpast form often looks ahead to an action or presents a standard procedure. The past form is common when recalling an event, but it may also present the first event as completed within a possible future situation. Do not choose mechanically according to the tense of the English translation.

Looking back on an occasion

前ぜん回かいお伺うかがいした際さいに、担たん当とう者しゃから詳くわしい説せつ明めいを受うけました。

When I visited last time, I received a detailed explanation from the person in charge.

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Using it with nouns

ご入にゅう館かんの際さいは、この券けんを係かかり員いんにお見みせください。

When entering the building, please show this ticket to an attendant.

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事じ故こ発はっ生せいの際さいの連れん絡らく手て順じゅんを確かく認にんしておきましょう。

Let us review the contact procedure to follow if an accident occurs.

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Before the following noun, use 際さいの.

Formal and everyday choices

とき is the broad, neutral choice for everyday “when.” 際さい is more formal and presents the situation as a defined occasion, so it fits official instructions much better than relaxed personal conversation.

駅えきに着ついたとき、電でん話わして。

Call me when you get to the station.

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This is the natural everyday choice.

会かい場じょうに到とう着ちゃくした際さいは、受うけ付つけにお申もうし出でください。

Upon arriving at the venue, please report to reception.

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The formal wording suits an official instruction.

More examples

契けい約やくを更こう新しんする際さいに、住じゅう所しょの変へん更こうも届とどけ出でました。

When I renewed the contract, I also reported my change of address.

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災さい害がいの際さいは、エレベーターを使し用ようしないでください。

In the event of a disaster, do not use the elevator.

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面めん接せつを受うけた際さい、勤きん務む開かい始し日びについて質しつ問もんされました。

When I had the interview, I was asked about my available start date.

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お申もうし込こみの際さいに必ひつ要ような書しょ類るいは、こちらでご確かく認にんいただけます。

You can check here which documents are required when applying.

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海かい外がいへ出しゅっ張ちょうする際さいの注ちゅう意い点てんをまとめました。

I compiled a list of points to keep in mind when traveling abroad on business.

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資し料りょうを持もち出だす際さいは、責せき任にん者しゃの許きょ可かを得えてください。

When removing documents from the premises, please obtain permission from the person responsible.

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