A control device for a motor drive system including an inverter converting DC voltage into AC voltage for driving an AC motor, comprising: current detection means for detecting motor current supplied to said AC motor; control method selection means ( S10-S30) for selectively setting a control method of said voltage conversion in said inverter, depending on an operation condition of said AC motor; first motor control means for performing torque control based on said motor current detected by said current detection means, when said control method selection means ( S10-S30) selects a first control method in which an applied voltage to said AC motor is controlled according to a sinusoidal pulse width modulation method by vector control; and second motor control means ( 200, 400) for performing torque control based on said motor current detected by said current detection means, when said control method selection means ( S10-S30) selects a second control method in which an applied voltage to said AC motor is controlled according to a modulation method of outputting a voltage with a fundamental component larger than said sinusoidal pulse width modulation method; characterized by rotational speed detection means for detecting a rotational speed of said AC motor; rotational speed change occurrence detection means for detecting that a rotational speed change of a prescribed value or greater occurs in said AC motor, during selection of said second control method, based on an output of said rotational speed detection means; and motor voltage correction means ( S120/320, S220/330, S230/245), when occurrence of a rotational speed change of said prescribed value or greater is detected by said rotational speed change occurrence detection means, for correcting the applied voltage to said AC motor by said second motor control means ( 200, 400) depending on said rotational speed change, wherein said motor voltage correction means ( S120/320, S220/330, S230/245) correct the applied voltage to said AC motor so as to be lowered, when a decrease of the rotational speed of said prescribed value or greater is detected. current detection means for detecting motor current supplied to said AC motor; control method selection means ( S10-S30) for selectively setting a control method of said voltage conversion in said inverter, depending on an operation condition of said AC motor; first motor control means for performing torque control based on said motor current detected by said current detection means, when said control method selection means ( S10-S30) selects a first control method in which an applied voltage to said AC motor is controlled according to a sinusoidal pulse width modulation method by vector control; and second motor control means ( 200, 400) for performing torque control based on said motor current detected by said current detection means, when said control method selection means ( S10-S30) selects a second control method in which an applied voltage to said AC motor is controlled according to a modulation method of outputting a voltage with a fundamental component larger than said sinusoidal pulse width modulation method; characterized by rotational speed detection means for detecting a rotational speed of said AC motor; rotational speed change occurrence detection means for detecting that a rotational speed change of a prescribed value or greater occurs in said AC motor, during selection of said second control method, based on an output of said rotational speed detection means; and motor voltage correction means ( S120/320, S220/330, S230/245), when occurrence of a rotational speed change of said prescribed value or greater is detected by said rotational speed change occurrence detection means, for correcting the applied voltage to said AC motor by said second motor control means ( 200, 400) depending on said rotational speed change, wherein said motor voltage correction means ( S120/320, S220/330, S230/245) correct the applied voltage to said AC motor so as to be lowered, when a decrease of the rotational speed of said prescribed value or greater is detected.