PURPOSE: To make automatic cleaning of inside a cleaning trough prior to attachment of 'black dirt' by sensing contamination of the trough walls, judging that intra-trough cleaning is needed, and informing in response to the output from this judging means.

CONSTITUTION: The degree of photo-permeation is measure 28 after the final dehydration 27 of normal cleaning processes 26 for washing clothes, followed by judgement by an electronic controller, and when the result becomes lower than the preset degree of photo-permeation, contamination of trough walls is informed by means, e.g., of an LED 31 of a display 30 arranged on a panel 29. By reference thereto an operator starts intra-trough cleaning. After water is supplied 14 into the trough, trough cleaning detergent is cast in 15, and upon agitation 16 leaving 17 is made as a process of cleaning. This is followed by agitating again 18, and water is exhausted 19. To rinse inside of the trough, water is supplied 20, and upon agitation 21 water is exhausted 22. The intra- trough cleaning processes except cast-in 15 of the detergent are executed automatically by the electronic controller.