To bring the teeth of a spline into contact at all times while transmitting large driving force by ensuring the transmission area of driving force and to smoothly conduct transmission in an excavator with an inclined and connected spline shaft.

Since a crowning 3 is executed to the teeth of a male spline 2, a tooth contact is generated at all times, a self centering effect that the center of the tooth contact is moved before and behind the center in the longitudinal direction of teeth and teeth is brought into contact equally is generated, and a contact area for transmitting driving force can be ensured. Since spline pairs at all opposed positions conduct the tooth contact, driving force is transmitted smoothly while the splines can correspond even to the change of connecting angles.