The vehicle-use power supply control apparatus includes a first battery supplying electric power to a load, an alternator driven by a vehicle engine, a second electric accumulator parallel-connected to the first battery, an electric power converter performing two-way power transmission between the first and second batteries, and a power supply control unit. The power supply control includes a function of setting a target power generation efficiency index, a function of setting a target power generation amount of the alternator on the basis of the target power generation efficiency index, while referring to a map defining relationship between a power generation efficiency index and a power generation amount of the alternator, and a function of controlling an amount and a transmission direction of transmission power of the electric power converter in order that an amount of electric power generated by the alternator becomes equal to the target power generation amount.