PURPOSE: To make the measurement of the degree of vacuum more accurate and to make the detection of gaseous pressure near a target possible by providing magnetic poles near the opening of a conduit communicating with a vacuum gage in such a way as to sandwich said opening.

CONSTITUTION: In a chamber of a sputtering device, magnetic poles are provided near the opening of a conduit communicating with a vacuum gage in such a way as to sandwich said opening. For example, the conduit of a vacuum gage 1 opens into a chamber wall 2, and a pair of magnetic poles 3 are mounted to the wall in such a way as to sandwich said opening. Then, in spite of flowing of the plasma flow 4 generated in the chamber toward the conduit, it is bent vertically by the magnetic field between the magnetic poles, whereby the plasma flowing into the vacuum gage is reduced and the influence that the plasma flow gives upon thermo electrons or ion current is substantially eliminated.