To solve a problem wherein a driving shaft tilts depending on a state of a road surface during running of a vehicle, and thus a seal boot deforms repeatedly in various directions, so that the seal boots easily break and replacing frequency is uneconomically increased.

A support bent surface 27 is formed on the outer peripheral surface in an opening side end of a bowl shaped part 15 of a constant velocity joint 5, the seal boot 21 is provided with a first mounting member 28 slidably engaging with the support bent surface 27, a second mounting member 29 of the seal boot 21 is slidably in the midway of the driving shaft 22 in the shaft core C direction. When the driving shaft 22 tilts, the first mounting member 28 slides on the support bent surface 27 and the second mounting member 29 slides on the driving shaft 22. Thus, even when the driving shaft 22 tilts and the seal boot 21 deforms repeatedly, an excessive force is prevented from applying to the seal boot 21.