To provide a power tool designed to make three-staged gear changes in the speed of output shaft rotation by means of a planetary gear-speed reduction device in an operation characterized by an excellent workability.

In the power tool, rotational speed is made changeable for each of the first carrier 8 and the second carrier 9, on the strength of the first change-over ring 20 and the second change-over ring 24, both of which can be slid in forward or backward directions. Within the power tool, meanwhile, a change-over plate 32, which can be slid in forward/backward directions from the exterior of a housing 2, is installed. Into slide grooves 34 and 34, formed on the change-over plate 32, the first protrusion 35 and the second protrusion 36 of the respective change-over rings are inserted in the manners in which they are movable in forward and backward directions, with coil springs 37 formed on their frontal and rear positions subsequently. Within the power tool, bottleneck portions 38, arranged to regulate the contact points of the coil spindle 37 with the protrusions 35 and 36, are installed differently at the frontal and rear positions between individual slide grooves 34 and 34. By altering the contact state of the coil spring 37 and the individual protrusions 35 and 36 in accordance with the sliding position of the change-over plate 32, the frontal and rear positions of the two change-over rings 20 and 24 are mutually rearranged to change the rotational speed of the spindle 6 into three stages.