a differential case;

side gears in pairs;

two or more pinion gears;

pinion gear support surfaces;

a boss part;

an oil introduction channel; and

a window,

the differential case being rotatable about a first axial line,

the side gears in pairs being supported by the differential case in a freely rotatable manner about the first axial line,

the two or more pinion gears being configured to (i) be supported by the differential case in a freely rotatable manner about at least one second axial line orthogonal to the first axial line and (ii) mesh with the respective side gears in pairs,

the pinion gear support surfaces being provided in an inner surface of the differential case and supporting back sides of the respective two or more pinion gears such that the two or more pinion gears freely rotate,

the boss part being provided to a side part of the differential case in a protruding manner, the side part being located on at least one side of the differential case in an axial direction, and the axial direction being a direction along the first axial line,

the oil introduction channel being provided to the boss part, the oil introduction channel being configured to introduce lubricating oil from an outside of the differential case to a corresponding one side gear support surface of side gear support surfaces in the inner surface of the differential case, the corresponding one side gear support surface being configured to support a back side of a corresponding one side gear of the side gears such that the corresponding one side gear freely rotates, and the corresponding one side gear being located on the same side of the differential case as the boss part,

the window being formed in the differential case so as to make an inside and the outside of the differential case communicate with each other, and

the inner surface of the differential case including main guide weirs, part, the oil guiding part being located between, in th the main guide weirs protruding from the inner surface toward the first axial line and enclosing an entire circumference of the window so as to guide at least some of oil such that the at least some of the oil deviates from a flow direction from the corresponding one side gear support surface to the window along the inner surface and flows around the window, the main guide weirs including a first weir, a second weir and a third weir, the main guide weirs is configured such that the first weir located between the corresponding one side gear support surface and a circumferential rim of the window, the second weir located between a corresponding other side gear support surface and the circumferential rim of the window, and the third weir located between a corresponding one pinion gear support surface of the pinion gear support surfaces and the circumferential rim of the window are integrally connected to each other.