a gear;

a differential case to which the gear is fixed on an outer peripheral surface so as to be integrally rotatable;

a differential pinion shaft that is inserted through a shaft support hole formed in the differential case and that is housed in the differential case such that an axial direction is along a direction perpendicular to a rotation axis of the differential case;

first and second pinion gears rotatably supported about an axis of the differential pinion shaft around both ends of the differential pinion shaft inside the differential case; and

first and second side gears that are disposed inside the differential case at a predetermined space, mesh with the first and second pinion gears, and are housed in the differential case so as to be rotatable with reference to an identical rotation axis to the differential case, wherein

a bulging portion having a flat surface perpendicular to the rotation axis of the differential case is provided at a central part of the differential pinion shaft, and the flat surface is brought into direct or indirect contact with an inner surface of at least one of the first and second side gears,

wherein an end surface and an opposite end surface of a fixing pin inserted in the fixing hole respectively face the first and second side gears,

the bulging portion is a holder through which the differential pinion shaft is inserted, and which has the flat surface on an end surface, and

stepped portions in which an outer peripheral end is reduced in a thickness direction are formed on both left and right side surfaces of the holder.