To provide a technique capable of easily detecting the abnormality of a measuring instrument fitted to a semiconductor production device.

A Penning vacuum gage 1 fitted to a dry etching device or the like is composed of two dependent first vacuum-degree detector 5a, and second vacuum-degree detector 5b, having the same type principle. The value 9 of a difference between an output value 7a from the first vacuum-degree detector 5a and the output value 7b from the second vacuum-degree detector 5b is output from an output-value comparator 8. When the value 9 of the difference exceeds a preset value, the abnormality of the Penning vacuum gage 1 is decided, and a control unit for the dry etching device is informed of the abnormality of the Penning vacuum gage 1.