An in-wheel motor drive device, comprising: a motor; a wheel bearing comprising a fixed ring, a rotation ring, and a plurality of rolling elements arranged between the fixed ring and the rotation ring; and a speed reducer configured to connect the motor and the wheel bearing to each other, the speed reducer being formed of a parallel shaft gear speed reducer comprising: a speed reducer input shaft (S in), which is configured to rotate integrally with a rotation shaft of the motor, and comprises an input gear; a speed reducer output shaft (S out), which is configured to rotate integrally with the rotation ring of the wheel bearing, and comprises an output gear; and an intermediate shaft (S m) comprising: a small-diameter intermediate gear configured to mesh with the output gear; and a large-diameter intermediate gear provided coaxially with the small-diameter intermediate gear, wherein the speed reducer is formed of a three-shaft two-stage parallel shaft gear speed reducer comprising the large-diameter intermediate gear and the input gear in mesh with each other, wherein the large-diameter intermediate gear has a circumscribed circle which is superimposed with a pitch circle of the plurality of rolling elements of the wheel bearing when viewed from an axial direction, wherein the large-diameter intermediate gear has a pitch circle diameter which is smaller than a pitch circle diameter of the output gear, characterized in that the speed reducer input shaft (S in), the intermediate shaft (S m), and the speed reducer output shaft (S out) are arranged so as to form a triangular shape when viewed from the axial direction, and wherein at least a part of the speed reducer input shaft (S in) in the axial direction is arranged in an axial region of the speed reducer output shaft (S out). a motor; a wheel bearing comprising a fixed ring, a rotation ring, and a plurality of rolling elements arranged between the fixed ring and the rotation ring; and a speed reducer configured to connect the motor and the wheel bearing to each other, the speed reducer being formed of a parallel shaft gear speed reducer comprising: a speed reducer input shaft (S in), which is configured to rotate integrally with a rotation shaft of the motor, and comprises an input gear; a speed reducer output shaft (S out), which is configured to rotate integrally with the rotation ring of the wheel bearing, and comprises an output gear; and an intermediate shaft (S m) comprising: a small-diameter intermediate gear configured to mesh with the output gear; and a large-diameter intermediate gear provided coaxially with the small-diameter intermediate gear, a speed reducer input shaft (S in), which is configured to rotate integrally with a rotation shaft of the motor, and comprises an input gear; a speed reducer output shaft (S out), which is configured to rotate integrally with the rotation ring of the wheel bearing, and comprises an output gear; and an intermediate shaft (S m) comprising: a small-diameter intermediate gear configured to mesh with the output gear; and a large-diameter intermediate gear provided coaxially with the small-diameter intermediate gear, a small-diameter intermediate gear configured to mesh with the output gear; and a large-diameter intermediate gear provided coaxially with the small-diameter intermediate gear, wherein the speed reducer is formed of a three-shaft two-stage parallel shaft gear speed reducer comprising the large-diameter intermediate gear and the input gear in mesh with each other, wherein the large-diameter intermediate gear has a circumscribed circle which is superimposed with a pitch circle of the plurality of rolling elements of the wheel bearing when viewed from an axial direction, wherein the large-diameter intermediate gear has a pitch circle diameter which is smaller than a pitch circle diameter of the output gear, characterized in that the speed reducer input shaft (S in), the intermediate shaft (S m), and the speed reducer output shaft (S out) are arranged so as to form a triangular shape when viewed from the axial direction, and wherein at least a part of the speed reducer input shaft (S in) in the axial direction is arranged in an axial region of the speed reducer output shaft (S out).