A voltage detector for a battery assembly having unit cells, the voltage detector includes a low voltage system circuit and a high voltage system circuit. The low voltage system circuit includes an enable pulse output unit which outputs an enable pulse to command detection of a voltage across both terminals of the unit cell. The high voltage system circuit includes a voltage pulse output unit which output a voltage pulse showing a voltage across both terminals of the unit cell, a switch which is provided between each unit cell of the battery assembly and the voltage pulse output unit and a switch controller which conducts ON-OFF control of the switch so that the each unit cell is successively connected to the voltage pulse output unit according to the enable pulse inputted from the pulse output unit.