is heated to the first preset temperature t 1 that is the washing stroke for removing dirt from the laundry is performed during the first preset time period t 1 s 20 at this time the anti yellow course controls the heater 41 to be turned on off alternatively and repetitively to thereby maintain the first preset temperature t 1 during performing the anti yellow course in the meantime if the user selects not the anti yellow course but a normal course a preset washing stroke time period t 0 is selected and the heater 41 is turned off whereby the washing stroke is performed during the preset washing stroke time period t 0 in state of turning off the heater 41 s 30 at this time preferably the first preset time period t 1 of the anti yellow course is longer than the preset washing stroke time period t 0 of the normal course on completing the washing stroke of the corresponding preset time period according to the washing course selected by the user rinsing and spin drying strokes s 40 and s 50 are performed in sequence the rinsing stroke s 40 is performed to rinse the laundry in the clean water to thereby remove detergent and contaminants from the laundry the spin drying stroke s 50 is performed by rotating the drum inner and outer tubs at a high speed to thereby remove the moisture from the laundry in detail the washing stroke of the anti yellow course will be explained with reference to fig5 first after measuring the amount of laundry s 21 the water.