A motor drive system for driving an AC motor mounted on a vehicle, and having an output shaft connected to a wheel of said vehicle for torque transmission, comprising: a motor drive circuit being capable of bidirectionally supplying and receiving a power to and from the AC motor; and motor control means for controlling an operation of said motor drive circuit to perform an operation of consuming a surplus electric power determined depending on a state of said motor drive system by said AC motor, and to perform a follow-up operation of causing an output torque to follow changes in torque command value (Tqcom) while keeping said operation of consuming the surplus electric power when said torque command value to said AC motor changes during said consuming operation, wherein said motor control means includes: current command producing means for producing, as a current command (Idcom, Iqcom), a set of a d-axis current command value and a q-axis current command value corresponding to an amplitude and a phase of a motor current causing the output torque of said AC motor to match with said torque command value and causing said surplus electric power to be consumed by said AC motor, current control means for controlling the operation of said motor drive circuit to generate the motor current in accordance with said current command produced by said current command producing means, and said torque command value is calculated from a requested output of said vehicle, and is set negative at a time of regenerative braking of said vehicle. a motor drive circuit being capable of bidirectionally supplying and receiving a power to and from the AC motor; and motor control means for controlling an operation of said motor drive circuit to perform an operation of consuming a surplus electric power determined depending on a state of said motor drive system by said AC motor, and to perform a follow-up operation of causing an output torque to follow changes in torque command value (Tqcom) while keeping said operation of consuming the surplus electric power when said torque command value to said AC motor changes during said consuming operation, wherein said motor control means includes: current command producing means for producing, as a current command (Idcom, Iqcom), a set of a d-axis current command value and a q-axis current command value corresponding to an amplitude and a phase of a motor current causing the output torque of said AC motor to match with said torque command value and causing said surplus electric power to be consumed by said AC motor, current control means for controlling the operation of said motor drive circuit to generate the motor current in accordance with said current command produced by said current command producing means, and said torque command value is calculated from a requested output of said vehicle, and is set negative at a time of regenerative braking of said vehicle. current command producing means for producing, as a current command (Idcom, Iqcom), a set of a d-axis current command value and a q-axis current command value corresponding to an amplitude and a phase of a motor current causing the output torque of said AC motor to match with said torque command value and causing said surplus electric power to be consumed by said AC motor, current control means for controlling the operation of said motor drive circuit to generate the motor current in accordance with said current command produced by said current command producing means, and said torque command value is calculated from a requested output of said vehicle, and is set negative at a time of regenerative braking of said vehicle.