A spindle lock device includes an engaging ring fixed in position relative to a body case of an impact screwdriver. A flat relief surface is definable on an outer circumference of the anvil that can be disposed inside of the engaging ring. An engaging member can be disposed between the engaging ring and the flat surface of the anvil. The engaging member can wedge between the engaging ring and an end portion in the circumferential direction of the relief surface of the anvil, so that the anvil is locked with respect to rotation relative to the body case.