A current balancer suitable for a multi-phase power converting device is provided. The current balancer includes an error detection unit and a plurality of pulse control units. Each of the pulse control units includes a current-to-voltage converter, a charging and discharging controller, a capacitor, and a comparator. The error detection unit detects a plurality of channel currents generated by the multi-phase power converting device, and generates a plurality of error currents by calculating. The charging and discharging controller provides a charging voltage or a discharging voltage according to a constant pulse-width modulation (PWM) signal. When the channel currents are balanced, the comparator generates a PWM signal with a constant duty cycle. When the channel currents are not balanced, an error voltage generated by the current-to-voltage converter is used to adjust a voltage level of the charging voltage or the discharging voltage, so that the PWM signal is varied correspondingly.