A control operation of correcting, based on a difference between a target value and a measured value of a controlled response time, a standby time from change in a set value of a flow rate to a value that is not zero until start of output of an opening signal is repeated. As a result, a response time for the flow rate to reach the set value of the flow rate after the set value changes can be a desired value independently of a type, the set flow rate, the temperature, and the pressure of fluid, individual differences among devices, and the like. The difference between the target value and the measured value of the controlled response time may be multiplied by a weight coefficient, and the control operation may be carried out for each of a predetermined plurality of ranges of the flow rate.