PURPOSE: To shorten the time until rotating speed of a drier becomes target rotating speed, and prevent a variation in the rotating speed by varying an adjusting width of supply electric power to be supplied to a motor on the basis of an inclination of a part corresponding to rotating speed of a motor at adjusting time in a motor torque curve.

CONSTITUTION: A microcomputer 37 finds a period of a pulse on the basis of a pulse signal from a rotary sensor, and detects rotating speed of a motor 10 from this period. Next, detecting rotating speed is subtracted from target rotating speed, and a rotating speed difference is found. When the rotating speed difference is, for example, not less than 30rpm and belongs to an A area in a motor torque curve, a correction value of the delay time of phase control is set in (-) 0.2msec, and when it is not leass than 30rpm and belongs to a B area, the correction value is set in (-) 0.15msec. When the rotating speed difference is less than 10 rpm and is not less than (-) 10rpm, the correction value is set in 0.