A lubricating oil temperature sensor to detect a temperature of a lubricating oil is provided in a lubricating oil passage in a speed reducer, a coil temperature sensor to detect a temperature of a motor coil is provided in a stator of an electric motor, and a rotation speed detection sensor to detect a rotation speed of the electric motor is provided. A control device includes: an abnormality detector to detect an abnormality in the lubricating oil temperature sensor; and a lubricating oil temperature estimator to estimate the temperature of the lubricating oil on the basis of a determined relationship using the temperature detected by the coil temperature sensor and the rotation speed detected by the rotation speed detection sensor, when the abnormality detector detects the abnormality in the lubricating oil temperature sensor.