A ratchet wrench is disclosed, which comprises a body unit which has a circular groove at its one side and a stop member; a head unit which includes a housing rotatably passing through a circular groove of the body unit, and a ratchet gear engaged at an outer rim of the housing and is selectively rotatable in one direction as the ratchet gear is engaged with the stop member; a worm screw which is rotatably pin-engaged in the interior of the housing; and a pair of arms of which one end of each arm is inserted into the interior of the housing and is pin-engaged therein with a thread being formed on an upper side of each arm and being engaged with the worm screw.