To prevent a reinforcing truss 3 from separating from a deck plate 1 with a locking tool 5.

A deck plate has a waveform cross section, upper and lower flanges 11 and 13, and an immediate web 7. The entire reinforcing truss has a triangle pole shape having isosceles triangle cross section, and comprises three end bars 25 and 27 that are disposed in the intermediate part between two facing webs of the deck plate orthogonally to the travelling direction of the waveform and are parallel in the isosceles triangle, and lattice bars 29 that are disposed on two side surfaces of the triangle pole shape, welded to the end bars, and arranged in a triangular and zig-zag shape. The locking tool 5 is a steel bar that is disposed on the upside of the right and left bottom bars of the reinforcing truss and has Z-like plane shape, and both ends 35 are locked in small grooves 9 formed in the webs of the deck plate. A spacer 37 formed of the steel bar disposed between the Z-like steel bar and the bottom end bar 27 has an upward U-shape in a vertical surface, and two Z-like immediate parts are welded to both U-shape tips 41.