GEAR FASTENING STRUCTURE

PROBLEM TO BE SOLVED: To provide a gear fastening structure capable of securing the mechanical strength of a fastened site even when a ring gear is fastened to a differential case after the ring gear is pressed into the differential case.SOLUTION: The gear fastening structure includes a differential case 13 having a flange 44, and a ring gear 12, the ring gear 12 pressed into the flange 44 being fastened to the flange 44. The flange 44 has a side face supporting part 51 and a caulking and fixing part 52. The caulking and fixing part 52 has an annular protrusion 61 having an abutment face part on which a caulking die abuts, and the ring gear 12 has an inclined face part. The abutment face part has a first end located on the side of a first side face part 34 in the direction of a rotation axis, and the inclined face part has a second end located on the side of the first side face part 34 in the direction of the rotation axis. In the state that the ring gear 12 is pressed into the flange 44, the first end of the abutment face part is located on the further side of the first side face part 34 than the second end of the inclined face part in the direction of the rotation axis.