An active gas generation apparatus comprising: an active gas generation electrode group including a first electrode component and a second electrode component provided below said first electrode component; an alternating-current power source unit configured to apply alternating-current voltage to said first and second electrode components (1A, 2A) so that said first electrode component is at high voltage, a discharge space being formed between said first and second electrode components through application of said alternating-current voltage by said alternating-current power source unit, wherein said discharge space is configured to be externally supplied with material gas, wherein said second electrode component is provided with a gas ejection port for ejecting active gas obtained by activating said material gas; a first auxiliary member (31-32, 41-42) provided to form an alternating-current voltage application space (R31, R41) between said first auxiliary member and said first electrode component, said alternating-current voltage application space (R31, R41), being separated from said discharge space; a second auxiliary member (33, 43) made of a non-metallic material and supporting said active gas generation electrode group from the side of said second electrode component, said second auxiliary member (33, 43) including an auxiliary member gas discharge port (33i, 33k, 43i, 43k) through which the active gas ejected from said gas ejection port passes; characterised by a housing (34, 44) made of metal that houses all of said active gas generation electrode group and said second auxiliary member (33, 43) and at least part of said first auxiliary member (31-32, 41-42), said housing (34, 44) including a housing gas discharge port (34k, 44k) through which the active gas passing through said auxiliary member gas discharge port (33i, 33k, 43i, 43k) is discharged to an outside, a housing contact space (R34, R44) separated from said discharge space and being provided between said housing (34, 44) and each of said first and second auxiliary members, wherein said first auxiliary member includes a material gas flow path (31h, 32h, 41h) for a material gas supply path, through which the externally supplied material gas is guided to said discharge space independently from said alternating-current voltage application space (R31, R41) and said housing contact space (R33, R34) so that gas flow in said discharge space and gas flow in said alternating-current voltage application space (R31, R41) are separated from each other and gas flow in said discharge space and gas flow in said housing contact space (R33, R34) are separated from each other. an active gas generation electrode group including a first electrode component and a second electrode component provided below said first electrode component; an alternating-current power source unit configured to apply alternating-current voltage to said first and second electrode components (1A, 2A) so that said first electrode component is at high voltage, a discharge space being formed between said first and second electrode components through application of said alternating-current voltage by said alternating-current power source unit, wherein said discharge space is configured to be externally supplied with material gas, wherein said second electrode component is provided with a gas ejection port for ejecting active gas obtained by activating said material gas; a first auxiliary member (31-32, 41-42) provided to form an alternating-current voltage application space (R31, R41) between said first auxiliary member and said first electrode component, said alternating-current voltage application space (R31, R41), being separated from said discharge space; a second auxiliary member (33, 43) made of a non-metallic material and supporting said active gas generation electrode group from the side of said second electrode component, said second auxiliary member (33, 43) including an auxiliary member gas discharge port (33i, 33k, 43i, 43k) through which the active gas ejected from said gas ejection port passes; characterised by a housing (34, 44) made of metal that houses all of said active gas generation electrode group and said second auxiliary member (33, 43) and at least part of said first auxiliary member (31-32, 41-42), said housing (34, 44) including a housing gas discharge port (34k, 44k) through which the active gas passing through said auxiliary member gas discharge port (33i, 33k, 43i, 43k) is discharged to an outside, a housing contact space (R34, R44) separated from said discharge space and being provided between said housing (34, 44) and each of said first and second auxiliary members, wherein said first auxiliary member includes a material gas flow path (31h, 32h, 41h) for a material gas supply path, through which the externally supplied material gas is guided to said discharge space independently from said alternating-current voltage application space (R31, R41) and said housing contact space (R33, R34) so that gas flow in said discharge space and gas flow in said alternating-current voltage application space (R31, R41) are separated from each other and gas flow in said discharge space and gas flow in said housing contact space (R33, R34) are separated from each other.