A battery mount device may include a housing to which a battery pack is detachably attached, and a cover attached to the housing so as to cover the battery pack and configured to open and close by rotating around a rotation axis. Force in a direction closing the cover may act on the cover in a state where the battery mount device is placed on a horizontal plane. The battery-mounted device may further comprise a cover holding mechanism capable of holding the cover in an open state. The cover holding mechanism may include a cover holder configured to move, in response to an operation by a user, between a holding position where the cover holder interferes with a rotating motion of the cover and a released position where the cover holder does not interfere with the rotating motion of the cover.