disclosed is a power control apparatus of a complex terminal which includes a main battery and an auxiliary battery . the power control apparatus includes : a dc / dc converter for outputting an auxiliary power supplied from the auxiliary battery after adjusting a level of voltage of the auxiliary power to a required input voltage level of the complex terminal ; a second voltage sensor for measuring voltage of a main power outputted from the main battery , and controlling the auxiliary power of the auxiliary battery to be inputted to the dc / dc converter before the measured voltage of the main power becomes lower than a predetermined voltage ; and a first voltage sensor for interrupting supply of the main power from the main battery to the complex terminal and controlling the auxiliary power outputted from the dc / dc converter to be supplied to the complex terminal , when the measured voltage of the main power becomes lower than the predetermined voltage .