Coin lockers in Japan are generally safe and easy to use. It’s convenient when you don’t want to walk around with heavy bags.
Coin lockers can be found at most of the train stations and sometimes in shopping buildings. They usually come in different sizes and the daily cost depends on the size. (Some lockers charge by certain hours e.g. by every six hours.) The cost is usually 300 yen for small, 400 yen for medium, 500 yen for large, and 600-700 yen for extra large lockers per calendar day.
When the price is fixed per calendar day, remember that you are paying up to the end of the day (12 am). For instance, let’s say you stored your bag at 7 pm in a small 300-yen locker. When you come back to open it after 12 am, you will have to insert additional 300 yens to unlock it.
Most of the lockers only accept 100 yen coins, but relatively new coin lockers will allow you to pay with 500 yen coins or IC cards such as Suica and Pasmo. Moreover, new ones are usually keyless. In that case, the PIN number printed on a receipt or the IC card you use to make a payment will function as a key when unlock.
Last but not least, don’t forget to take out your bag! You can usually store up to 3 days. If the locker is left locked for more than 3 days, the train station staff will unlock it to empty it.