PURPOSE: To prevent leakage of water from inside a cooking chamber in an easy manner by a method wherein a voltage is applied between electrodes of a shaft member consisting of a piezoelectric material to make the outer circumferential part of the shaft member partly undergo repeated expansion and shrinkage so as to cause the shaft member to slide on the inner surface of a bearing with an effect to rotate a turntable.

CONSTITUTION: A microwave radiation is emitted from a magnetron 19 into a cooking chamber 13 and a turntable 15 is rotated. The turntable 15 is driven by a drive circuit (voltage-applying means) 28 which applies a voltage between electrodes 24 of a shaft member 23. This application of a voltage is based on the piezoelectric properties of the shaft member 23, that is, the voltage is applied in such a manner as to form electric fields in directions in which, between adjacent electrodes 24, the shaft member 23 expands at the circumferential part and shrinks at the opposite part and the switching is so made as to cause the expansion and the shrinkage to successively alternate in one direction circumferentially. The shaft member 23 is placed in sliding contact with the inner surface of a bearing 22 so that the friction imparts a rotative force in one direction that rotates the turntable 15. Since the shaft member 23 itself does not rotate, no clearance is required between the shaft member 23 and a through hole 25 therefor so that a seal can be formed by using a sealing material 26 therebetween.