An in-wheel motor drive device includes an electric motor section, a speed reducer section, a wheel bearing section, and a casing. The speed reducer section includes a speed-reduction structure using a parallel shaft gear. The parallel shaft gear includes an input shaft, which is coupled to the electric motor section, an input gear, at least one intermediate shaft including input-side and output-side intermediate gears, an output shaft, which is coupled to the wheel bearing section, and a final output gear. The input, intermediate, and output shafts are supported by rolling bearings to be rotatable. At least two rolling bearings configured to support the intermediate and output shafts on an out-board side and two rolling bearings configured to support the intermediate and output shafts on an in-board side are arranged at positions at which respective bearing widths are prevented from being superimposed with each other in an axial direction.