To provide a power tool having a rapid fastening device capable of fastening and unfastening operations without requiring large operating effort of a user and ensuring both of a fastening position and a replacing position, colts a low manufacturing cost.

This power tool allows a fixed lever 6 to rotate around a rotating spindle 9 between the fastening position where a tool 3 is unrotatably fixed around a hollow spindle 2 and the replacing position and the tool 3 is disposed between a fixed flange 7 attachable to the side end part of the tool of a fixed spindle 4 and the hollow spindle 2. A sliding element 8 having a line of a radial distance (a) coming into contact with the fixed spindle 4 at a rotational angle αto the longitudinal axis of the fixed spindle 4 by the rotation of the fixed lever 6 around the rotating spindle 9 in provided. The fixed spindle 4 is provided with a contact surface 11 having a span K extending in a rotational direction. The span K is set so as to be at least sin (α) times the distance (a).