To provide a suspension system support structure of a low floor bus capable of expanding the width of a cabin passage floor near front tires.

This structure is equipped with tire house members 22 for covering the front tires 5 from the upper side, a floor member 23 connected to the right and left tire house members 22 so as to cover the front tires 5 from the cabin center side and forming the cabin passage floor F, a front axle 18 for pivoting the front tires 5, and air springs 20 mounted on the upper ends of axle spring sheets 19 projecting upward from the front axle 18. In the structure, chassis spring sheets 24 are installed on top part under surfaces of the tire house members 22, and upper ends of the air springs 20 are jointed to the chassis spring sheets 24, to keep rigidity of a suspension system 4 mounting target part of a chassis frame, and simultaneously to enable expansion of the width B2 of the cabin passage floor F near the front tires 5.