PURPOSE: To make the completion time of all operations constant to the utmost by detecting the water supply capacity through a water supply means for supplying water into a washing tank, and starting a rinsing operation ealier as the time when it is decided that the water supply capacity is low by the detected result, thereby starting the rinsing operation in accordance with the water supply capacity.

CONSTITUTION: When water supply is started by opening a water supply valve 16, a controller 19 measures the time when a water level in a washing tank reaches a prescribed water level and detects the water supply capacity, based on a water level detecting signal from a water level sensor 17 for detecting the water level in the washing tank. Also, the controller 19 controls so that a rinsing operation is respectively started earlier and later, in the case it is decided that the water supply capacity is low, and on the contrary, in the case it is decided that the water supply capacity is high. In such a way, the completion time of all operations can be made constant to the utmost, and it can be prevented that the washing is left as it is and creased.