To realize securing of a maximum inflow amount of compressed air and a fine regulation of an inflow amount without increasing a pulling load of a trigger lever.

A valve stem 28c is slidably inserted into a pilot valve 22. One end of the valve stem 28c can be pushed from the outside by passing through a bottom part of a valve housing 27 of the pilot valve 22. The valve stem 28c is provided so that a space S between the bottom part of the pilot valve 22 and the valve housing 27 may be successively movable to a first position communicated with a supply passage 18, a second position communicated with the atmosphere, and a third position communicated with the atmosphere and capable of pushing a regulating valve 21 at the other end of the valve stem 28c.