A technique is provided which improves durability in a power tool having a torque transmission device. The representative power tool has a torque transmission device 151. The torque transmission device 151 includes a projection 171 formed on one of opposed surfaces of a first rotating member 153 and a second rotating member 155 and protruding in a direction of a rotational axis, a recess 161 for receiving the projection 171, which is formed in the other of the opposed surfaces and recessed in the direction of the rotational axis, a projection-side engagement surface 175a formed on the projection 171, and a recess-side engagement surface 165a formed on the recess 171. Torque is transmitted when the projection-side and recess-side engagement surfaces 175a, 165a are engaged with each other, while the torque transmission is interrupted when the projection-side and recess-side engagement surfaces 175a, 165a are disengaged from each other. The projection-side and recess-side engagement surfaces 175a, 165a are inclined at a predetermined angle β with respect to normals P of the first and second rotating members 153, 155.