PURPOSE: To facilitate the changing over of an air supply to two different loads through one air route.

CONSTITUTION: Air blow supply piping for a pallet seating air blow B1 and an air blow B2 for an automatic tool length unit 7 is provided from one pressure air source E through a common pressure controller 2 and a switch valve V1, and a throttle valve V3 is insertedly provided in the air blow B2 for the automatic tool length unit 7 to weaken blasting pressure, and when the switch valve V1 is actuated to open at the time of pallet exchanging motion and during automatic tool length measurement, it supplys the pressure air as the air blow on the side of low circulation resistance.