PURPOSE: To eliminate useless air blow-off by a method wherein, a workman enters a shower-room by opening an entrance door after confirming that an exit door is completely closed, and the air blowing is started for a prescribed period of time when the entrance door is closed.

CONSTITUTION: When the inlet side door is at first open for entering a clean room, a limit switch DS1 turns on in order to actuate a relay 1X, a ratchet relay 2X, resulting in self-holding the circuit of a relay 3X. When the inlet side door is next closed, the relay DS1 turns off and as a result the relay 1X is also turned off, however the magnet switches of a fan motor 52F and a timer T are actuated through the self-hold circuit of the relay 3X, resulting in blowing-off an air shower for a set time. When the outlet side door is open at the end of the air shower, a limit switch DS2 turns off and as a result said relay 2X is operated so as to turn off its contact. Finaly when the outlet side door is closed, the limit switch DS2 turns off, resulting in stopping the operation of the relay 2X so as to restore the original state of the air shower room.