a body having a motor housing, a handgrip, and a gear housing, the gear housing having a driving member and a hammer drive member, the hammer drive member having an upper gear and a lower gear positioned within the gear housing so as to be rotatable in opposing directions on a longitudinal axis wherein one working stroke comprises one rotation of the upper gear and the lower gear;

a motor disposed in the motor housing;

a trigger;

an interlocking member;

a hammer having an upper and a lower engagement projection;

a compression coil spring;

an operating device having a first mode, a second mode, a trigger switch biased into an off position, and an internal switch biased into an off position, the trigger switch and the internal switch operatively connected for completing one working stroke after finishing the first mode and the second mode, the first mode comprising the internal switch moving to an on position by interlocking with the trigger switch while the trigger switch is in an on position, the trigger switch being activated to the on position in response to a linear depression applied to the trigger, thereby energizing the motor for a predetermined period of time as the first mode, before de-energizing the motor after the predetermined period of time as beginning the second mode, the second mode comprising the internal switch releasing its interlocking position with the trigger switch and returning to the off position in response to the predetermined period of time ending, and the trigger switch remaining in the on position during the second mode;

a cam block provided in the internal switch adapted to linearly move with depressing operation of the trigger; and

a switch arm provided in the internal switch rotatably adapted for rotation by the cam block, biased by a first torsion spring.