It has been found to be disadvantageous that, with a conventional pressure type flow control apparatus, it is not possible to determine the state of a valve on the downstream side of a throttle mechanism with a flow rate output signal due to the structural reason of the apparatus. To overcome the difficulty, the determination of whether a valve on the downstream side of a throttle mechanism is open is achieved at ease using the state of changes of a flow rate output signal while a pressure type flow control apparatus is in operation. With a pressure type flow control apparatus, a valve on the downstream side of a throttle mechanism is released and a flow rate setting value Qe to be inputted to a pressure type flow control apparatus is changed to detect the magnitude V of changes of a flow rate output signal Qo from a pressure type flow control apparatus while said flow rate setting value Qe changes so that it is determined either that a valve on the downstream side of a throttle mechanism is opening normally in the case that the magnitude V of changes of said flow rate output signal Qo is found to be above the predetermined value, or that the releasing operations are malfunctioning in the case that the magnitude V of changes is found to be below the predetermined value.