PURPOSE: To save water consumption to a great extent by a method wherein an imitation sound is produced when a user sits on a toilet seat, and water is started to flow inside a toilet bowl for a specified period of time for washing while the imitation sound is cut off when the user gets up from the toilet seat.

CONSTITUTION: When a user sits on a toilet seat, a controller 10 receives a turning-on signal from a sitting sensor 8 and outputs a driving signal to an imitation sound producing circuit 11, and thereby an imitation sound is given out of a speaker 9. When the user gets up on finishing the use of a toilet, the sitting sensor 8 is turned off, then the controller 10 stops the output of the driving signal to the imitation sound producing circuit 11 and drives an actuator 4 to open a water supply valve 3 for washing the inside of a toilet bowl 1. In the case where the user pushes an operating button 7 on sitting on the toilet seat, the imitation sound is not produced. Then water is started to flow inside the toilet bowl 1 for a specified period of time when the user pushes the operating button 7 again on finishing the use of the toilet. Therefore, water-saving can be made certainly.