A battery housing portion S includes regulating members 30 adapted to fit grooves of a battery pack having a T-shape cross section, so that the battery pack can be housed in the battery housing portion S in the state that the both regulating members 30 fit the grooves. The regulating members 30 regulate housing orientation of the battery pack 20, so that misjudgment about orientation of the battery pack 20 is prevented. In addition, if the orientation has been misjudged, an operator can notice such misjudgment immediately, thereby improving the operability during mounting the battery pack 20.