To improve drying performance and to reduce drying time, by rotating a drum at a specific kind of rotation speed, detecting an exhaust temperature for each rotation speed, searching a rotation speed corresponding to the lowest temperature among detected temperatures to make it the rotation speed of the drum.

Power is supplied to a drum motor 22, a fan motor 13, and a heater 19 to start drying operation. A drum rotation speed control circuit 38 is activated to drive the drum to rotate in at least two kinds of rotation speeds changed every several seconds to ten and several seconds. Drum exhaust temperature at each rotation speed is measured by a temperature sensor and a temperature measuring circuit 35 and stored in a memory 36. A main control circuit 32 set the drum rotation speed to make the exhaust temperature to be the lowest among measured exhaust temperatures as the drum rotation speed and controls the drum motor 22. After continuing the rotation for a prescribed time, the operation is repeated. Thus the drying speed is increased and the time is shortened.