A battery voltage equalizer circuit for equalizing battery voltages among a plurality of battery cells in a serial connection is disclosed. The battery voltage equalizer circuit includes a battery voltage equalizer unit having a plurality of equalizer parts, wherein each equalizer part, coupled to a positive terminal and a negative terminal of a corresponding battery cell, is conducted with an equalization current upon a receipt of an equalization signal, and a battery voltage detector unit, coupled to the positive and negative terminals of the plurality of battery cells, generates the equalization signal so as to conduct the battery voltage equalizer unit as long as a voltage of any one of the battery cells reaches an equalization voltage.