To provide a steel-concrete synthetic floor slab, by which the lowering of a reinforcement at a time when an operator mounts can be prevented without using an excessive supporting member such as a trestle and a steel-plate reinforcing material for holding dead load before composition can be reduced, and its execution method and a bridge using the composite floor slab.

A rational stiffening truss structure with a steel plate 15, a long-sized stud 18 and reinforcements (a distributing bar and a main reinforcement) is constituted by placing the distributing bar 16 on the head section 18b of the long-sized stud 18 and fixing the distributing bar 16 onto the head section 18b by using an applying bar 22 and a hoop band 21 and fixing the main reinforcement by using the hoop band to the distributing bar at a crossed section with the distributing bar. The floor slabs for the bridge are configured by using the steel-concrete composite floor slabs.