To limit the left/right pivoting of a front axle case within a constant angle even if the vertical clearance between a front frame and the front axle case is varied.

A rear part of a pivot frame 4 is vertically pivotably supported on a front part of a vehicle body 2 around a support shaft 5 in a left/right direction, the front axle case 6 for suspending a front wheel 26 is left/right pivotably supported on the pivot frame 4 around a center shaft 7 in a longitudinal direction, and left and right suspension cylinders 8 for the front wheel 26 are provided on the front frame 3. A pivoting restriction part 36 having a receiving surface 36A is provided on the pivot frame 4, a restriction part to be pivoted 37 having an abutment surface 37A abutted on the receiving surface 36A when it is left/right pivoted to the front axle case 6 is provided.