Power tool

A power tool, comprising:

• a motor having a motor shaft that is rotatable in a normal direction and in a reverse direction;
• a gear speed reducer that (i) is operably coupled to the motor shaft and (ii) includes at least one planetary gear mechanism, each of the at least one planetary gear mechanism including a sun gear, an internal gear, a carrier and a plurality of planetary gears;
• a one-way clutch that is (i) in a transmission path from the motor shaft to a first sun gear of the at least one planetary gear mechanism and (ii) configured to permit rotation of the first sun gear relative to the one-way clutch while the motor shaft rotates in a first direction and to rotate integrally with the first sun gear while the motor shaft rotates in a second direction, the first direction being one of the normal direction and the reverse direction, the second direction being the other of the normal direction and the reverse direction;
• and
• a lock mechanism that is (i) operably coupled to the one-way clutch and (ii) configured to lock a first internal gear of the at least one planetary gear mechanism to be non-rotatable while the one-way clutch permits the relative rotation of the first sun gear and to cause the first internal gear to rotate integrally with the first sun gear while the one-way clutch rotates integrally with the first sun gear,
• wherein the gear speed reducer is configured such that a reduction ratio of the gear speed reducer is changed in response to (i) a change of a rotation direction of the motor shaft and (ii) a change of the number of the least one planetary gear mechanism that functions effectively.