To provide a pneumatic power tool for cutting a work by reciprocating a blade.

A power tool 10 has a main body 12. The main body 12 has a hollow internal section and a passage extended along the main body 12. The hollow internal section has first and second ports set in first and second positions away from each other to alternately introduce air. The tool has a connector for connecting a pneumatic hose to the tool to supply compressed air to the same. A throttle 30 is disposed in the passage to selectively supply compressed air from the passage. A valve is disposed along the passage, and guides air alternately from the first and second to press the inside in corresponding one of the first and second positions. The tool includes a piston unit 120 having a head housed in a space between the first and second positions to reciprocate the unit between extending and pulling-in positions. One of the piston unit 120 and the main body has a groove parallel to the axis of the unit, and the other has a projected portion engaged with the groove to prevent the rotation of the unit against the main body.