To provide a structure for fixing a precast floor slab, which shortens a period of time until construction is completed.

In a fixing structure for fixing precast floor slabs 2 to steel beams 1 and connecting the adjacent precast floor slabs 2 with each other, in a bridge in which the plurality of precast floor slabs 2 are installed in the bridge axial direction on the steel beams 1 each having an I-shaped or H-shaped cross section, the precast floor slab 2 has a haunch steel material 31 having an I-shaped or H-shaped cross section formed integrally with the underside of a haunch 2a which is a thickness increased part formed matching the position of the steel beam 1, the precast floor slab 2 is fixed to the steel beam 1 by superposing the haunch steel material 31 on the steel beam 1 and fastening them by a bolt and nut, a steel material 32 for joint having an I-shaped or H-shaped cross section is arranged orthogonally to the bridge axial direction with respect to the steel beam 1, and the ends of the adjacent precast floor slabs 2 are connected with each other via one steel material 32 for joint.