Traditional energy storage systems having lithium-ion battery cells or electric double-layer capacitors (EDLCs) connected in series require a separate charger and cell voltage equalizer. To simplify these energy storage systems, in this paper a transformer-less pulse width modulation (PWM) buck converter integrating a cell voltage equalizer using a voltage multiplier is proposed. The switch count is only two in the proposed converter because of the switchless voltage multiplier. An inductor in a conventional PWM buck converter is replaced with two inductors in the proposed converter in order to produce square wave voltage with an arbitrary amplitude, by which the voltage multiplier is driven. A charge-discharge cycling test using the prototype for three EDLCs connected in series was performed, and the results demonstrated the integrated functions of the proposed converter.