[Task] To allow a secondary battery built in a bio-signal measuring instrument (a wearable biosensor) to be charged without using a dedicated charging terminal.[Solution] A bio-signal measuring device includes: a battery as an internal power source and a charging circuit (200) for the battery； electrodes (10a, 10b) which are brought into contact with the skin surface of the human body at the time of bio-signal measurement and are connected to a predetermined power feeder (2) at the time of charging of the battery； a bio-signal processing circuit (100) which processes bio-signals detected at the electrodes (10a, 10b) in a predetermined manner； and a bio-signal and feed power distribution means (300), in which the bio-signal processing circuit (100) and the charging circuit (200) are switchably connected to the electrodes (10a, 10b) through the bio-signal and feed power distribution means (300), and at the time of the charging of the battery, the electrodes (10a, 10b) are used as charging terminals.
