To determine normality or abnormality of a differential pressure-pressure composite sensor on the basis of a single evaluation indicator.

A method includes: fully closing a flow rate control valve and then letting a secondary side open to the air, thereby causing measurement pressure P2 applied to a differential pressure sensor chip 43 of a differential pressure-pressure composite sensor 4 to be equal to the air, in which event the differential pressure sensor chip 43 and a pressure sensor chip 46 are applied with fluid pressure at the primary side of the flow rate control valve as measurement pressure P1; then obtaining a differential pressure signal ΔP and a static pressure signal PG respectively from the differential pressure sensor chip 43 and the pressure sensor chip 46; calculating the difference between differential pressure ΔP and static pressure PG obtained from the signals as an evaluation indicator ΔPG; and outputting an abnormality signal if the evaluation indicator ΔPG exceeds a usage limit value, or outputting a sensor replacement signal if the evaluation indicator ΔPG exceeds a switching threshold (where it is smaller than the usage limit value).