If you are involved in accident in Europe, you have to dial 112 for emergency but not in Japan. Unfortunately, Japan does not have single number for police, ambulance and fire brigade. Instead of 112, you have to dial 110 for police, 119 for ambulance and fire brigade.
Then, if you call 119, the operator will ask you if you need an ambulance or fire engine. Most of the countries dispatch their ambulances from hospitals or ambulance station but ambulances in Japan are dispatched from local fire departments. Therefore if you pass fire department in Japan, you can see red fire engines and white ambulances parked at the fire department.
If you rent a car and involved in car accident in Japan, you have to call 110, the police. Although Japan has National Police Agency, NPA does not dispatch their officers to the accidents and therefore local police will arrive and investigate the accidents.