To prevent creep deformation of a member due to an urging force for urging a cover in an opening direction and to improve the workability of assembling in the attaching of the cover by reducing the number of components.

A cover 23 covering an opening section for attaching or detaching a battery is openably supported by a cover support member 31. The cover support member 31 supports the cover 23 such that the cover 23 can be slidden at a prescribed amount in the closed condition and the cover 23 can be rotated after the sliding. While the cover 23 is in the closed condition, a projection 23a formed on the cover 23 is placed on a first position where the projection 23a is not urged by a projected section 32b. When the cover 23 is slidden, the projection 23a is displaced to be on a second position where it is urged by the projected section 32b.