<p>A hammer drill includes a motor; a spindle (5) rotatingly driven by the motor and holding an output bit (50); a motion conversion member (2) for converting rotational movement of the motor to reciprocating movement; a striker (35) reciprocatingly driven by the motion conversion member (2) for applying an axial striking force to the output bit (50); a striking-motion-releasing mechanism for releasing the striking force applying action exercised by the striker (35); and a tightening-torque adjusting clutch (4) for interrupting the transfer of the rotational force to the output bit (50) by increasing a load torque.</p>
