PURPOSE: To confirm the existence of a press-fit object by feeding air to the press-fit bar inserting section of a press-fit guide and detecting the air pressure change with a pressure switch when pressing a pin with a press-fit bar.

CONSTITUTION: When a piston 30 is moved by a stroke sufficient to press-fit a pin 3 into a hole 2, a bar 12 provided on a piston rod 11 hits a stopper 13, and further movement is restricted. On the other hand, as soon as a cylinder 9 is operated, compression air is fed to an air hole 6 from an air source 15 through a pipeline 14. If the pin 3 exists, the relief path of this compression air is blocked, thus the pressure value is increased. If the pin 3 does not exist due to a work mistake or the like, the compression air escapes to the outside through the notch 8a of a press-fit bar 8 and the small-diameter section 5b of a hole 5, thus the pressure value is not increased. These conditions are detected by a pressure switch 16.