Even when power supply to a gas supply target device is stopped and then resumed, the state of gas supply to a chamber is grasped and a process is performed in accordance with the state. The gas supply target device includes a retaining unit 12 which is able to selectively take one of three states A to C each indicating a state of gas supply to the chamber 10a and is able to maintain, when power supply to the gas supply target device is stopped, one of the states at stop of the power supply, when power supply to the gas supply target device is stopped and then resumed, in which one of the states A to C the retaining unit 12 is set is determined, and a process is performed in accordance with the state of the gas supply to the chamber 10a.
