A paper battery for connection to terminals protruding in same direction has positive and negative electrode plates joined together by a sealing agent therebetween formed with an insulating sheet. A hole penetrating one of the electrode plates and the insulating sheet to reach the other electrode plate and another hole penetrating the other of the electrode plates to reach the insulating sheet are provided such that not only is the battery connected properly to the terminals when it is inserted correctly but also a short circuit will be avoided even if the paper battery is inserted in upside-down direction.