A motor control system comprising: a boost converter configured to turn a plurality of first switching elements (13, 14) on/off at a predetermined carrier frequency to boost voltage of a battery and obtain boosted direct-current electric power; an inverter configured to turn a plurality of second switching elements (31, 32) on/off at a predetermined carrier frequency to convert the boosted direct-current electric power output from the boost converter to alternating-current electric power, the inverter supplying the alternating-current electric power to a motor; and a control unit configured to adjust boosted voltage of the boost converter, wherein the control unit includes an optimal boosted voltage map configured to define optimal boosted voltage (VHs) for operating the motor with a required number of revolutions and required torque, characterized in that the optimal boosted voltage (VHs) is a first voltage (VHs 1) that is lower than a system maximum voltage (VHmax) when the number of revolutions of the motor is between 0 and a first number of revolutions (N 1); the optimal boosted voltage is a second voltage that is lower than the first voltage when the number of revolutions of the motor exceeds the first number of revolutions but is equal to or smaller than a second number of revolutions; and the optimal boosted voltage increases to a voltage between the second voltage and the system maximum voltage in accordance with the number of revolutions of the motor when the number of revolutions of the motor exceeds the second number of revolutions, and the control unit is configured to set the boosted voltage of the boost converter to a voltage which is higher than the first voltage (VHs 1) defined by the optimal boosted voltage map, when the number of revolutions of the motor is between 0 and the first number of revolutions (N 1) and the carrier frequency (Fc) of the inverter is equal to or lower than a predetermined threshold value (Fc 0). a boost converter configured to turn a plurality of first switching elements (13, 14) on/off at a predetermined carrier frequency to boost voltage of a battery and obtain boosted direct-current electric power; an inverter configured to turn a plurality of second switching elements (31, 32) on/off at a predetermined carrier frequency to convert the boosted direct-current electric power output from the boost converter to alternating-current electric power, the inverter supplying the alternating-current electric power to a motor; and a control unit configured to adjust boosted voltage of the boost converter, wherein the control unit includes an optimal boosted voltage map configured to define optimal boosted voltage (VHs) for operating the motor with a required number of revolutions and required torque, characterized in that the optimal boosted voltage (VHs) is a first voltage (VHs 1) that is lower than a system maximum voltage (VHmax) when the number of revolutions of the motor is between 0 and a first number of revolutions (N 1); the optimal boosted voltage is a second voltage that is lower than the first voltage when the number of revolutions of the motor exceeds the first number of revolutions but is equal to or smaller than a second number of revolutions; and the optimal boosted voltage increases to a voltage between the second voltage and the system maximum voltage in accordance with the number of revolutions of the motor when the number of revolutions of the motor exceeds the second number of revolutions, and the control unit is configured to set the boosted voltage of the boost converter to a voltage which is higher than the first voltage (VHs 1) defined by the optimal boosted voltage map, when the number of revolutions of the motor is between 0 and the first number of revolutions (N 1) and the carrier frequency (Fc) of the inverter is equal to or lower than a predetermined threshold value (Fc 0).