PURPOSE: To enable to raise the temperature of air in an exhaust passage promptly and safely, by carrying cooling air for cooling a high-frequency oscillator to a heating chamber after passing through an air passage with a heater and a heat-insulating space defined between the air passage and the wall of the heating chamber dividedly in a high-frequency heating apparatus having a temperature sensor and a humidity sensor.

CONSTITUTION: Simultaneously with starting of cooking, a cooling fan 5 and a heater 16 are set into operation for heating air in an exhaust passage to a set temperature while detecting the temperature of air by a temperature sensor. In the arrangement of this invention, air in the exhaust passage is carried into a heating chamber 2 by passing a part of air flow produced by the cooling fan 5 through an air guide 7 and a heat-insulating space 17 dividedly and them mixing the divided flows. When the temperature of air in the exhaust passage is kept at the set temperature, a high-frequency oscillator 3 is set into operation. With such an arrangement, it is enabled to ensure safe operation of the apparatus by preventing over-heating of the wall of the heating chamber, to raise the temperature of air in the exhaust passage promptly, and to enhance accuracy of detecting the cooking conditions.