To provide a structure for connecting cylindrical shafts (side gears 10, 11 of differential 1) and rotating shafts (drive shafts 2, 3) by spline fitting, capable of keeping a state free from rattling in the rotating direction at a spline fitting part for a long period while comparatively easily and surely mounting and demounting them regardless of the total fitting length.

Teeth 2a, 3a of at least two parts at circumferential equal internal of male splines of the rotating shafts 2, 3 have the stepped twisted shape having the approximate same lead angles θ1, θ2 in a state of displacing tip-side areas 21, 31 and base-side areas 22, 32 in parallel with each other in the circumferential direction. The teeth 10b, 11b and grooves 10c, 11c of female splines of the cylindrical shafts 10, 11 have the linear shape along the axial direction O. The stepped twisted teeth 2a, 3a are press fitted.

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