PURPOSE: To prevent the momentary interrupt of a power source by the addition of an impact force and the supply of the reversed polarity power source by the reversed insertion of a battery by providing three curved pieces on a contact piece 3 consisting of a plate, providing a block on the third curved piece, and pressing it onto the plus electrode.

CONSTITUTION: A plate consisting of a conductive elastic member is turned up, whereby first and second curved pieces 5A, 5B for nipping a fixed wall 6B by a contact piece 5 pressed onto the plus electrode 2 of a battery 1 and a third curved piece 5C to be pressed onto the plus electrode 2 are provided. When a coil spring 4 is compressed by an impact force, the curved piece 5C follows it so that no space is formed between the curved piece 5C and the electrode 2 by the spring force of the curved piece 5C, and the momentary interruption is prevented. The curved piece 5C has a block 7 consisting of an insulating material to form a guide wall. This, since no power supply is performed even if the battery is reversely inserted, the supply of the reversed polarity power source is prevented.