the present disclosure provides a power control apparatus of a construction machine , including : an engine connected to a hydraulic pump to drive the hydraulic pump ; and a controller for calculating an engine load ratio defined as a ratio of a load torque of the engine for an engine maximum torque calculated from an input engine target rpm , and calculating an engine rpm command value according to the engine load ratio such that the engine is driven at the target rpm to output the calculated engine load ratio and engine rpm command value to the engine .