A power generation control apparatus of a rotating electrical machine for a vehicle is obtained which achieves load response control in a plurality of electric power generation control modes even if a generation voltage final target value rapidly changes. The apparatus includes a power control unit 103 and a storage battery 104 connected to a rotating electrical machine 102, and a rotation speed detection part 105 for detecting a rotational speed Na. The power control unit 103 controls power generation in a first mode when the rotational speed Na during operating as a generator is less than or equal to a predetermined value, and controls power generation in a second mode when the rotational speed Na is higher than the predetermined value. The power control unit 103 includes a generation voltage command value calculation section 111 that sets generation voltage command values Vr1, Vr2 for the individual modes, respectively, so as to follow a final target value to the storage battery 104, and a generation voltage update calculation command section 110 that instructs update timing tn, an amount of increase dH and an amount of decrease dL of each generation voltage command value to the generation voltage command value calculation section 111 based on the states of the rotating electrical machine and of the storage battery.