an upper cap mounted at an upper end of a housing, the upper cap having holding protrusions formed at left and right inner surfaces thereof;

a head support having left and right walls, pivot supporting recesses centrally dented at upper ends of the walls, respectively, lower coupling grips formed at outer surfaces of the respective walls, and hooks formed below the lower coupling grips, respectively, the hooks being configured to be caught by the holding protrusions of the upper cap;

a waterproof rubber plate mounted in the center of the upper end of the housing, the waterproof rubber plate having a center hole and a corrugated portion;

a guide plate mounted in the upper cap, the guide plate having an elongated center guide hole;

a vibrator slidably coupled into the elongated guide hole of the guide plate, the vibrator having a coupling pin formed at an upper end thereof and a clevis recess formed in a lower end thereof, as an eccentric shaft coupled to a motor is slidably coupled into the clevis recess, the vibrator being adapted to perform a leftward and rightward reciprocating motion;

a swing head having pivots configured to be fitted into and supported by the pivot supporting recesses of the head support, upper coupling grips formed at left and right outer surfaces thereof, and an arcuate trimmer drive slot perforated in the bottom thereof for allowing the coupling pin of the vibrator to be slidably coupled thereinto; and

a locking knob coupled to the upper cap through an elongated knob guiding slot perforated in the upper cap to thereby be slidable leftward and rightward, the locking knob having a latch configured to be detachably coupled into a holding groove formed at a lower surface of the swing head.