To reduce a floor impact sound by a heavy article generated in a detached house, a low-rise apartment, etc.

The composite floor slab having a floor slab 1a, a damping material 2a, a tabular material 3a and a peripheral constraint material 4 and reducing a floor impact sound by a heavy article is provided. In the composite floor slab, the damping material 2a is connected closely to the underside of the floor slab 1a, the tabular material 3a is attached closely with the underside of the damping material 2a, the peripheral constraint material 4 constrains at least one of the peripheral section of the floor slab 1a or a section in the vicinity of the peripheral section, and the vibrations of the floor slab 1a are damped.