To reduce a lateral size of an air nailing machine and to quickly leak pressure more than set pressure (pressure on a secondary side) to prevent the pressure more than the set pressure of the pressure reducing valve from being applied to the nailing machine, regarding the air nailing machine mounted with the pressure reducing valve capable of reducing compressed air of high pressure to a region of normal pressure.

A mounting screw of the pressure reducing valve is changed from a taper screw to a flat screw, and a switching valve relief groove is provided. As a result, the air nailing machine 60 mounted with the pressure reducing valve capable of sufficiently supplying air to the nailing machine and surely working a relief function can be obtained.