PURPOSE: To obviate the welding of a joining member to absorb an installation error of a joining part and simplify the working process by arranging H-shaped joists in square spaces formed of left and right frames, cross beams and center frames by joining longitudinal joist members to the cross beams.

CONSTITUTION: In a floor structure for a bus body, lateral frames 2 are joined between the front and rear ends of left and right side frames 1, and plural cross beams 3 are joined at specific intervals in the longitudinal direction between the frames 1. Center frames 4 in parallel to the left and right side frames 1 are arranged. In this case, H-shaped joists 11 formed by joining lateral joist members 10 between two parallel longitudinal joist members 9a and 9b are arranged in square spaces 8 formed of constitutional members 1, 3 and 4 by joining to the cross beams 3 while situating the longitudinal joist members 9a and 9b in parallel to the respective constitutional members 1 and 4. Thereby, a joining member to absorb an installation error of a conventional joining part can be obviated.