The power management method performed by the power management apparatus includes switching an operation mode of the power management apparatus from a standby mode to a normal mode when a voltage of the power management apparatus operating in the standby mode increases from a first upper limit value to a second upper limit value, switching the operation mode of the power management apparatus to a minimum operation mode when the voltage of the power management apparatus decreases to a first lower limit value while operating in the normal mode, switching the operation mode of the power management apparatus to a sleep mode when the voltage of the power management apparatus decreases to a second lower limit value while operating in the minimum operation mode, and switching the operation mode of the power management apparatus to the standby mode while operating in the sleep mode.