Abstract: A pneumatic tool for turning screws and nuts has a tool body including a driving member mounted rotatably thereon and capable of being pneumatically rotated. A ratchet wrench unit includes a crank and a swing arm. The crank has a crankshaft journaled in the ratchet wrench unit, and a crankpin. The swing arm is mounted rotatably in the ratchet wrench unit and is connected slidably to the crankpin so that the swing arm can be swung by the crankpin. The ratchet wrench unit is connected removably to the tool body in such a manner that the crankshaft can be rotated by the driving member. Instead of the ratchet wrench unit, a screwdriver may be mounted removably on the tool body in such a manner that the screwdriver can be rotated by the driving member.