PURPOSE: To surely inspect and monitor abutment of a positioning element on a workpiece by operating a signal device by a pressure sensor in the case of the pressure below a prescribed value.

CONSTITUTION: A positioning element 1 is provided with a fluid flow passage 2 for a gas-like medium, and the mouth 3 of the flow passage 2 faced to a workpiece can be closed directly with the workpiece or the pressure part abutting on the workpiece. The other end part of the fluid flow passage 2 is connected to a pressure fed device through a hose. This pressure feed device is provided with one blocking device and one pressure sensor placed in rear of the blocking device in the flowing direction of the medium, for the each connected positioning element. In the case of the pressure below a prescribed value, the pressure sensor operates a signal device.