A pivot shaft includes a shaft member having a male screw portion to be thread-connected to a vehicle body frame, and a nut member having a female screw portion to be thread-connected to part of a male screw portion of the shaft member corresponding to a projecting thread portion projecting from the vehicle body frame. The nut member as a locknut is attached so as to prevent the rotation of the adjusted shaft member. The locknut is a nut member formed into a cap-shape or a ball-head locknut shape. A tool engaging portion to which a multi-purpose tightening tool can be engaged is formed on the nut member. Since the multi-purpose tool can be engaged with the tool engaging portion on the nut member accurately, control of a tightening torque is facilitated, and the number of steps for controlling the tightening torque can be reduced.