To provide a pinion shaft and a differential device preventing interference to the pinion shaft with a ring gear of a differential case when attaching and detaching the pinion shaft with respect to the differential case, capable of reducing replacement costs and improving efficiency in replacement work of a pinion gear and a side unit housed in the differential case, and capable of preventing deterioration of strength of the differential case by minimizing the size of an opening window.

A differential device 11 has the pinion shaft 31 rotatably supporting the pinion gears 33, 34 attached at a certain interval in the interior of the differential case 12, the pinion shaft 31 is composed of split shafts 40, 41, 42 split via split parts 40a, 41a, 41b, 42a substantially orthogonal to an axial direction, and the split shafts 40, 41, 42 are composed smaller than the opening areas of opening windows 12j, 12k and smaller than a separation distance of the pinion gears 33, 34.

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