To provide a vehicular propulsion shaft having an axially expandable slide structure which is capable of reducing play in the slide structure according to the traveling condition of a vehicle.

When a propeller shaft 24 is expanded, a male spline tooth 50 of a first shaft 46 is engaged with a female spline tooth 56 of a second shaft 48 only in a part thereof. Since an inner circumferential surface of an annular projecting part 60 provided on a cylindrical part 54 presses an outer circumferential surface of an annular projecting part 64 provided on the second shaft 48, a cylindrical shaft end of the second shaft 48 is deformed inward of the radial direction. Thus, a space in the radial direction between the male spline tooth 50 and the female spline tooth 56 is reduced to reduce a play in the radial direction and a play in an oblique direction.