In input/output power control apparatus and method for a secondary battery, in a case where neither a current sensor nor a voltage sensor fails, allowable input/output powers which are an allowable input power by which the secondary battery allowably inputs and an allowable output power by which the secondary battery allowably outputs are calculated on the basis of an input and/or output current and a terminal voltage of the secondary battery and, in a case where the failure in either one of the current sensor and the voltage sensor is detected, the allowable input/output powers are calculated on the basis of a detected value of one of the current and voltage sensors in which no failure is detected, and each of input and output powers of the secondary battery is limited to be equal to or smaller than the corresponding one of the allowable input/output powers.