01
What it is
Otsu4 (App Store name: 危険物乙4 問題集) is an iPhone and iPad study app by Rivership, an indie studio in Tokyo, for the Class 4 (乙種第4類) hazardous materials handler exam in Japan. The app is written in Japanese; there is no English interface.
The question bank follows the three exam subjects: laws and regulations, basic physics and chemistry, and properties and fire fighting. The questions are original and based on the published syllabus; actual exam questions are not included.
02
Questions this app answers
- Is there a practice-question app for the Japanese 乙4 exam? Yes. This app has original questions for the three subjects. It is in Japanese.
- How is the 乙4 pass line handled? The app shows your accuracy per subject against the 60% line for each of the three subjects.
- Is there a mock exam? Yes: 35 questions (laws 15, physics and chemistry 10, properties and fire fighting 10), judged per subject.
- Can I study offline? Yes. The app works offline.
- Is it a subscription? No. It is a one-time purchase without ads.
03
Features
- Accuracy per subject: distance to the 60% line for each of the three subjects.
- Spaced-repetition review: missed questions return at set intervals.
- 35-question mock exam: laws 15, physics and chemistry 10, properties and fire fighting 10.
- Offline: questions are stored on the device.
- Home screen widget: a WidgetKit widget is included.
04
What it does not do
- It does not include real exam questions; the questions are original.
- It is not an official app of the exam organization and is not affiliated with it.
- It has no English interface.
05
Price
Otsu4 is free to download with a sample of the questions (20 questions). A single one-time purchase unlocks the rest. There is no subscription and no ads. The price is shown in the app and on the App Store.
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Privacy and data
Study progress stays on the device. No account is needed and there are no ads.
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Independent study aid
This app is made by Rivership and is not affiliated with the organization that administers the exam. The questions are original and based on the published syllabus.
08
FAQ
What is Otsu4?
A Japanese-language iPhone and iPad question-bank app for the Class 4 hazardous materials handler (乙種第4類) exam.
Are these real exam questions?
No. They are original questions based on the published syllabus.
Is it official?
No. It is an independent study aid.
Does Otsu4 (危険物乙4 問題集) work offline?
Yes. Questions, explanations and the mock exam work offline.
How much does Otsu4 (危険物乙4 問題集) cost?
Otsu4 is free to download with a sample of the questions (20 questions). A single one-time purchase unlocks the rest. There is no subscription and no ads. The price is shown in the app and on the App Store.
Does Otsu4 (危険物乙4 問題集) send my data anywhere?
Study progress stays on the device. No account is needed and there are no ads.
Which languages and devices are supported?
Japanese only. iPhone and iPad with iOS 17.0 or later.
iPhone & iPad · iOS 17.0+ · Version 1.0.9