PURPOSE: To discharge the hydrogen and oxygen gases generated in a battery during a charging process from an open exhaust hole and prevent a rise of the internal pressure of an implement and any explosive combustion in the implement by providing said exhaust hole that acts as a communication path between the inner space of the implement and the atmosphere and is freely opened and closed.

CONSTITUTION: When a discharge port 48 is blocked or a part of it is damaged or when there is a great deal of gas to be generated during charge and the gas is leaked into the space within the mainframe housing, a thin partition piece 21 that partitions the inner part of the mainframe housing into a motor housing section and a battery housing section is provided integratedly on a base 2 on which a motor 6 and a battery 7 are mounted and the hydrogen and xoygen gases generated in the battery 7 are hard to flow into the motor housing section. Besides, an exhaust hole 62 is provided at the bottom of the mainframe housing adjoining a recessed place 49 in which a terminal 25 is arranged. This exhaust hole 62 is normally closed by a valve axis section 63 that is provided on a level 26 so as to enclose the space within the mainframe housing and is opened by connecting to it a charge adapter in which a charge circuit is enclosed.