An automatic high-frequency heating apparatus of a composite type which comprises a heat source such as an electric heater or a gas burner for heating food by heat radiation or convection and a microwave source such as a magnetron for effecting microwave oscillation, and wherein both heating sources are energized and deenergized alternately, a sensor detects water vapor and/or a gas emitted from the heated food, and control means operates to automatically terminate the heating operation of the heating apparatus upon lapse of at least the time required before the sensor detects the emission of at least a predetermined amount of water vapor and/or a gas within a predetermined time period.