Provided is a heat treatment apparatus that even when annealing SiC at high temperature, can exhibit a low heat capacity and perform uniform heating. The heat treatment apparatus includes a pair of parallel plate electrodes, high-frequency power supply that applies a high-frequency voltage to the pair of parallel plate electrodes so as to discharge between the pair of parallel plate electrodes, a temperature measurement instrument that measures the temperature of a sample to be heated which is disposed in the pair of parallel plate electrodes, a gas introduction unit that introduces a gas to the pair of parallel plate electrodes, reflection mirrors that surround the pair of parallel plate electrodes, and a control unit that controls the output of the high-frequency power supply. Heating of a gas due to discharge between the pair of parallel plate electrodes is used to thermally treat the sample to be heated.