際（に）when; on the occasion of
The formal とき, for any occasion, even a routine one. It is the usual "when" of notices, announcements and service language: when you get off, when you apply, in an emergency.
When you enter the building, please show this ticket to a staff member.
When I visited last time, the person in charge gave me a detailed explanation.
How to form it
Noun + の + 際（に）／plain verb + 際（に）
The verb is in the dictionary form or the た-form, chosen as before とき. 際は usually leads into an instruction.
- Before it
- Something that is done or that happens, often with お or ご: ご利用の際, お降りの際, 緊急の際, 申し込む際.
- After it
- A request or an instruction, or what was done on that occasion.
- Where you'll meet it
- Station and in-flight announcements, signs, manuals, forms, business email.
In use
When touring the building, please show your ID at reception.
If anything goes wrong with the equipment, switch off the power immediately.
The た-form, as before とき: first the fault, then the switch.
In the event of a disaster, do not use the elevator.
I have put together some points to bear in mind when traveling abroad on business.
Before a noun, 際の.
Two things to know
とき in a formal voice
A friend says とき. A notice or a staff member says 際, and the rest of the sentence is formal to match.
Watch your step when you get off.
A parent to a child.
Please watch your step when you get off.
The announcement on the bus.
An occasion, not a time of life
際 needs something that is done or that happens, not a stretch of your life.
Not said: 学生の
(When I was a student, I lived in Kyoto.)
学生のとき or 学生のころ.
Close neighbours
ときN5
The everyday word, in casual and polite conversation alike.
Please turn off the light when you go to bed.
に際してN2
"On the occasion of" one particular, weighty event, as it happens or just before. The event can be one nobody wanted, such as a disaster.
As I step down, I would like to thank you sincerely for your many years of support.
にあたってN2
"On setting out to do" something big: what you do, or should bear in mind, at the outset.
In applying for the scholarship, I revised my research proposal from top to bottom.
Check yourself
1Which would you send to a friend?
Choose an answer to see why.
2Which sentence sounds natural?
Choose an answer to see why.
More detail
この際 is a set phrase of its own: "now that the moment has come".
Now that the moment has come, I will say it plainly.
More sentences
When I renewed the contract, I also reported my change of address.
You can check here which documents you need when you apply.
At the interview, I was asked about my start date.
When taking documents off the premises, please get permission from the person responsible.
Let's go over the contact procedure in case of an accident.