PURPOSE: To simplify a backlash preventing structure for a spline by a method wherein a C-type spring is relatively non-rotatably fixed to a spline-fitting-in shaft and on the sleeve side of a sleeve and teeth formed on the inner side of the spring are brought into pressure contact with the teeth of a shaft spline.

CONSTITUTION: In a rotation transmission shaft, a shaft 11 and a sleeve 12 have respective end parts which are spline-fitted in each other and one end of a C-type spring 13 with which a shaft 11 is surrounded is relatively non- rotatably fixed to the end face of the sleeve 12 by means of a pin 14. The C-type spring 13 is caused to generate a given tight binding force by the characteristics of a shape and a material. A tooth 13a subtracting a tooth height from a positive shift or a standard spline is formed on the inner side of the spring in the same module as those of the shaft 11 and the sleeve 12. Each tooth 13a is brought into pressure contact with both of adjoining teeth 11a of the spline of the shaft 11 through the resilient force of the spring 13. This constitution prevents the generation of a rotation backlash between the spring 13 and the shaft 11 and between the sleeve 12 and the shaft 11.