A method of controlling a driving force generation system for a vehicle, said driving force generation system including a power line (MPL, MNL), a plurality of power storage units (6-1, 6-2) electrically connected in parallel with said power line (MPL, MNL), a rotating electric machine (34-1, 34-2) capable of bi-directionally converting electric power and rotational driving force, a power converting unit (30-1, 30-2) connected between said power line (MPL, MNL) and said rotating electric machine (34-1, 34-2), for performing power conversion between said rotating electric machine (34-1, 34-2) and said power line (MPL, MNL), and a single voltage converting unit arranged between said power line (MPL, MNL) and said plurality of power storage units (6-1, 6-2); said control method comprising the steps of: obtaining temperatures (Tb1, Tb2), voltage values (Vb1, Vb2), and current values (Ib1, Ib2) of said power storage units (6-1, 6-2); calculating the state of charge (SOC1, SOC2) of said power storage units (6-1, 6-2) based on said temperatures (Tb1, Tb2), voltage values (Vb1, Vb2), and current values (Ib1, Ib2) of said power storage units (6-1, 6-2); determining allowable charging power and allowable discharging power in each of said plurality of power storage units (6-1, 6-2), based on said state of charge (SOC1, SOC2) of each of said plurality of power storage units (6-1, 6-2); calculating a sum of said allowable charging powers of each of said power storage units (6-1, 6-2) and a sum of said allowable discharging powers of each of said power storage units (6-1, 6-2); determining a target load power value such that it does not exceed said sum of said allowable charging powers and said sum of said allowable discharging powers; determining a first ratio in a range between 0 and 1 based on state of charge of each of said plurality of power storage units (6-1, 6-2); determining a second ratio in a range between 0 and 1 based on temperature of each of said plurality of power storage units (6-1, 6-2); multiplying said target load power value by said first and second ratios (K1, K2) to determine a limited target load power value; determining a target voltage value (Vh*) by making a reference to a rotational speed (MRN1, MRN2) of said rotating electric machine (34-1, 34-2); generating commands to said power converting unit (30-1, 30-2) so that the power exchanged between said power line (MPL, MNL) and said rotating electric machine (34-1, 34-2) attains to said limited target load power value; and generating a switching command for said voltage converting unit so that the voltage value (Vh) appearing at the power line (MPL, MNL) attains said target voltage value (Vh*), wherein the above steps are repeatedly executed as long as said vehicle is in an ignition on state. obtaining temperatures (Tb1, Tb2), voltage values (Vb1, Vb2), and current values (Ib1, Ib2) of said power storage units (6-1, 6-2); calculating the state of charge (SOC1, SOC2) of said power storage units (6-1, 6-2) based on said temperatures (Tb1, Tb2), voltage values (Vb1, Vb2), and current values (Ib1, Ib2) of said power storage units (6-1, 6-2); determining allowable charging power and allowable discharging power in each of said plurality of power storage units (6-1, 6-2), based on said state of charge (SOC1, SOC2) of each of said plurality of power storage units (6-1, 6-2); calculating a sum of said allowable charging powers of each of said power storage units (6-1, 6-2) and a sum of said allowable discharging powers of each of said power storage units (6-1, 6-2); determining a target load power value such that it does not exceed said sum of said allowable charging powers and said sum of said allowable discharging powers; determining a first ratio in a range between 0 and 1 based on state of charge of each of said plurality of power storage units (6-1, 6-2); determining a second ratio in a range between 0 and 1 based on temperature of each of said plurality of power storage units (6-1, 6-2); multiplying said target load power value by said first and second ratios (K1, K2) to determine a limited target load power value; determining a target voltage value (Vh*) by making a reference to a rotational speed (MRN1, MRN2) of said rotating electric machine (34-1, 34-2); generating commands to said power converting unit (30-1, 30-2) so that the power exchanged between said power line (MPL, MNL) and said rotating electric machine (34-1, 34-2) attains to said limited target load power value; and generating a switching command for said voltage converting unit so that the voltage value (Vh) appearing at the power line (MPL, MNL) attains said target voltage value (Vh*), wherein the above steps are repeatedly executed as long as said vehicle is in an ignition on state.