A motor drive device having drive controller to control a motor for driving an electric vehicle wheel depending on position of magnetic poles using angle detection value sensed by a motor angle sensor; motor angle estimator to estimate an angle of a motor rotor without a rotation sensor; sensor malfunction determiner to determine malfunction of the sensor; sensor switcher to cause the controller to control using an estimation value of the rotor angle estimated by the estimator instead of the angle detection value sensed by the sensor once the determiner determines that the sensor malfunctions; and start-up rotor angle calculator to calculate an angle of the rotor from a counter electromotive voltage of the motor and to cause the controller to control using the calculated angle, when the motor is started up after stop of the motor in a state where the sensor is determined as malfunctioning by the determiner.