PURPOSE: To attempt the increase of strength of a floor plate and the decrease of vibration by forming upwardly convex protruding streak parts in the center area, positioned on the upper part of at least a tractor car body, of a floor plate, and forming recessed parts for covering the protruding streak parts on the back surface of a floor mat.

CONSTITUTION: A floor mat 4 made of rubber or elastic plastic is placed on the upper surface of a floor plate 3 for covering the upper surface of a tractor car body 2, and the right and left parts on the upper surface are taken as step parts 5, and the center part is taken as a foot placing part 6. In such floor structure, an opening 31 is formed in the center area of the floor plate 3, and a cover plate 32 is fixed by a bolt so as to block this opening 31, and the maintenance and check of a transmission is performed by releasing the opening 31 by detaching this cover plate 32. In this cover plate 32, several laterally long protruding streak parts 29 are formed in the longitudinal direction by press working, and recessed parts 30 for covering the protruding streak parts 29 are formed on the back surface of the floor mat 4.