PURPOSE: To enable to make heat treatment evenly, with high precision and at high speed, by a method wherein a material to be heated, which is placed on a stage constituted rotatably and reciprocally in the right and left directions, is provided in a resonance part of a cavity and made to position on a resonance point of a microwave.

CONSTITUTION: Resin tablets 1 are mounted on rotary rollers 2, 3 and a primary rotary speed value and a laterally movement speed value are set by a drive control part 18. A primary microwave output value is set similarly on a control part 14 of a microwave output. On the one hand, a heating temperature value and a heating time value of the resin tablets 1 are set on a measuring treatment part 17 of a temperature. When a main device is operated under the above-mentioned state, the resin tablets 1 are moved laterally at a predetermined speed while they are being revolved at the predetermined number of revolutions and heated by a microwave output at a resonance point of a cavity wherein field strength reaches a maximum.