PURPOSE: To protect both of inner and outer tubes from flying stone and an impact and prevent deformation and breakage and dislocation of a protector with which the inner tube is covered.

CONSTITUTION: Inner and outer tube protectors 18 and 19 with which outer and inner tubes 7 and 8, respectively, are covered in a longitudinal direction. When the front tube is shrunk, the inner tube protector 19 is overlapped with the outer tube protector 18. A slide engaging means 24 to regulate other movement than relative slide in a longitudinal direction between the two protectors 18 and 19 is formed throughout the overall length of a maximum lap margin length between the two protectors. The slide engaging means 24 comprises a guide groove 25 formed along the longitudinal direction of the outer tube protector 18 and a guide rail 26 formed along the longitudinal direction of the inner protector 19, and a guide rail 26 is slidably engaged with the guide groove 25.