To provide a terminal voltage detector for battery which does not need an input line to an operational amplifier to be cut off, even if a control power source is in an off state.

The terminal voltage detector for battery 10 is provided with a battery pack 12 having a plurality of unit cells 12a-12c of a secondary battery connected in series with each other, an operational amplifier 18 detecting the terminal voltage accommodated in each cell, a control power source VCC providing a driving power source for the operational amplifier 18, and a bypass circuit 22 which consists of a resistance 14 with which a positive electrode end of each cell and a control power source line are connected so that a driving power source can be provided for an operational amplifier 18 when a control power source is off, and a diode 18, and moreover, is connected with a feedback resistor 26 between the input side negative electrode end and the output end side. For that reasons, since a switch part to cut off a voltage detection line from secondary battery cells, which a combination battery consists of, is unnecessary, a space-saving, low-cost terminal voltage detector for a battery can be provided.