To improve waterproofness more while securing assembling performance by the housing of a half-split structure, thereby eliminating the possibility of reduction in waterproofness caused by a gap generated by an external force applied from a rotary operation member when a power tool such as an electric polisher required of waterproofness includes the housing of the half-split structure on the left and right.

In a part of the housing 20 of a half-split structure on the left and right, i.e., a portion to which the external force of a left-right separation direction is applied by a rotational operation, cylindrical parts 23 and 24 not formed into half-split structures are arranged to improve waterproofness.