To reduce vehicle weight by securing prescribed rigidity and strength of a step support part by an increase in little work manhours without using a stay.

A step 12 is arranged in a side part of a cab of a vehicle, and a rear part of this step is supported by a rear step support 13b. A front splashboard 18 is arranged in front of front wheels so as to extend in the car width direction. The outside edge of this front splashboard is installed on the inside edge of the rear step support, and the upper edge of the front splashboard is fixed to an under surface of a floor panel 14a of the cab. A bead 18d downwardly inclining toward the car width directional outside is formed on the front splashboard. The inside end of this bead is positioned on the board upper edge, and the outside end of the bead is constituted so as to be positioned on the board outside edge in the vicinity of the step.