Abstract: An active gas generator that generates active gas by activating supplied material gas through discharge in a discharge space formed between a high-voltage side electrode component and a ground side electrode component of an active gas generation electrode group. A combined structure of covers completely separates the discharge space from an alternating-current voltage application space, and includes, independently from the alternating-current voltage application space, a material gas flow path for a material gas supply path, through which externally supplied material gas is guided to the discharge space. A housing contact space formed between a metal housing and each of the covers and an electrode component installation table is completely separated from the alternating-current voltage application space and the discharge space.