PURPOSE: To automate discharge operation by providing a rotary valve disc, which opens and shuts a discharge port by pivoting by the use of an electric motor, to a valve seat provided to the upper end of the discharge port.

CONSTITUTION: When a user leaves a water closet after stool, a switch 18 is controlled, and when the switch 18 is controlled in a control position in the case of stool, a controller 17 drives a gear motor 16 to make an output gear 15 perform normal rotation, and a valve disc 10 is rotated approximate 90° from the original position. After that, when the valve disc 10 rotates approximate 90° for the sake of a half spherical bowl shape, about a half of the opening of a valve seat 11 is opened, and washing water stored in a low tank flows to the inside of a coupling pipe 8 through a discharge port 4 from the opening of the valve seat 11 to wash the water closet. Then, by the operation of a timer 19, at a time after the elapse of a certain time, the controller 17 makes the motor 16 perform reverse rotation to restore the valve disc 10 to the original position, and the rotation of the motor 16 is stopped to shut the discharge port 4.