A differential gear to be mounted on a vehicle, comprising a pair of side gears, at least two pinion gears meshed with the side gears, and a differential case that houses the side gears and the at least two pinion gears, lubricating oil being supplied to and discharged from an inside of the differential case via an opening portion, wherein the differential case includes at least two seat surfaces formed on an inner peripheral surface of the differential case so as to support the pinion gears, weir portions (53a, 53b) provided between the adjacent seat surfaces and extending in a direction along a rotational direction of the differential case to connect between the adjacent seat surfaces, and an oil reservoir portion formed on the inner peripheral surface by the weir portions (53a, 53b) so as to be positioned on an opposite side, in an axial direction of the differential case coaxially corresponding to an axial direction of the side gears, of the opening portion from a first weir portion of the weir portions (53a, 53b); and a ring gear is fixed to the differential case; characterised in that a pinion washer is disposed between a back surface of each of the pinion gears and the seat surface; an oil introduction port is formed in each of the seat surfaces, the oil introduction port communicating with the oil reservoir portion on a front side in the rotational direction of the differential case at a time when the vehicle travels forward and at least partially overlapping the pinion washer as seen in an axial direction of the pinion gear; the differential case includes a guide portion that guides the lubricating oil in the oil reservoir portion toward the oil introduction port on an opposite side of the ring gear side by narrowing the oil reservoir portion as the oil reservoir portion extends away from the ring gear in the axial direction; and the oil introduction port is formed in the seat surface so as to be proximate to a center of the seat surface in the axial direction. the differential case includes at least two seat surfaces formed on an inner peripheral surface of the differential case so as to support the pinion gears, weir portions (53a, 53b) provided between the adjacent seat surfaces and extending in a direction along a rotational direction of the differential case to connect between the adjacent seat surfaces, and an oil reservoir portion formed on the inner peripheral surface by the weir portions (53a, 53b) so as to be positioned on an opposite side, in an axial direction of the differential case coaxially corresponding to an axial direction of the side gears, of the opening portion from a first weir portion of the weir portions (53a, 53b); and a ring gear is fixed to the differential case; characterised in that a pinion washer is disposed between a back surface of each of the pinion gears and the seat surface; an oil introduction port is formed in each of the seat surfaces, the oil introduction port communicating with the oil reservoir portion on a front side in the rotational direction of the differential case at a time when the vehicle travels forward and at least partially overlapping the pinion washer as seen in an axial direction of the pinion gear; the differential case includes a guide portion that guides the lubricating oil in the oil reservoir portion toward the oil introduction port on an opposite side of the ring gear side by narrowing the oil reservoir portion as the oil reservoir portion extends away from the ring gear in the axial direction; and the oil introduction port is formed in the seat surface so as to be proximate to a center of the seat surface in the axial direction.