The apparatus according to the invention is adapted for transcutaneous treatment by gas. The apparatus (10) comprises a rigid-wall cabinet (20) and having an upper opening and at least one openable panel, wherein a seat (25) is arranged inside the cabinet (20), and the cabinet (20) comprises at least one gas concentration measurement unit (29a), and the cabinet (20) further comprises a gas inlet (30) for feeding the treatment gas and a gas outlet (31 ) for discharging the treatment gas； a gas supply unit (40) coupled to the gas inlet (30) of the cabinet (20) via a pipe (41 ) and through an interposed controllable valve (42)； and a gas tank (50) connected to the gas supply unit (40). The apparatus further comprises a ventilation unit (60) connected to the gas outlet (31 ) of the cabinet (20) through an interposed controllable valve (63), said ventilation unit (60) being coupled via a further pipe (62) to a space (70) hermetically separated from the room containing the cabinet (20), and wherein said ventilation unit (60) is designed so that it can discharge the entire volume of the treatment gas from the inner space of the cabinet (20) within at most 5 seconds. The apparatus further comprises a control unit (80) for receiving the signals of the gas concentration measurement unit (29a) and for controlling operation of the valves (42, 63) and said ventilation unit (60) based on at least the signals of the gas concentration measurement unit (29a).
