PURPOSE: To prevent the infiltration of muddy water or the like from a cotter pin portion for fixing a king pin, in the front axle of a vehicle.

CONSTITUTION: An O ring 7 or a gasket is interposed in the engaged surface between a cotter pin 4 and a front center 2, a gasket 9 or the O ring 7 is interposed in the engaged surface between a nut 6 and the front center 2 side end, and also a sealant 12 is interposed in the screw engaging part between a male screw part 4A on the outer peripheral surface of the cotter pin 4 end part and a female screw part 6B on the inner peripheral surface of the nut 6.