Koban is a distinguished Japanese style of police box. Usually 2- 3 police officers are staffed in the single Koban.
Koban belongs to the regional police station which belongs to prefectural police department. Koban are mostly located where many people gather. For example, train stations.
In case an incident happens near the Koban, the police officer from the Koban rushes to the crime scheme. Or if you found a lost item on the street, you have to take it to the nearest Koban. Koban is also used as the place where you can ask the way. If you are lost, or do not know where is the store, you can ask the police officer at the Koban the way to the store.
Police stations in Europe is quite hard to recognize. May be there is a small sign on the wall but police station in Japan always is a single building which exists only for police function. Then, Koban is also a single small hut which is easily to find.
Japan has the one of the highest arrest ratios in the world, but the prevention of crimes are also high, thanks to the Koban. Which means tourists can enjoy Japan without being involved in trouble.
The photo is the Koban in Chichibu, Saitama. Seibu Chichibu station Koban belonging to Chichibu police department. There are several posters of crime prevention. Usually Japanese most wanted criminals are posted there too.