We have performed experimental examinations for the purpose of proposing a floor finishing structure with superior effects in terms of combating heavy-weight floor impact sound. We have developed a box floor with ease of construction and excellent heavy-weight floor impact sound insulation performance and examined its effect with a 1200 × 1200 mm test piece connected to inter-noise 2020. The box floor has a floor finishing structure with anti-vibration and sound insulation measures aimed at improving measures against heavy-weight floor impact sound. We herein report the results of a basic examination on the reduction of the transmitted heavy-weight floor impact sound of a box floor structure in a reinforced concrete wall construction testing device when the area is further expanded to about 10 ?. As a result, with the air layer under the box floor open, the floor impact sound level was reduced by 9 dB in the 63-Hz band compared to the bare surface. In addition, with the air layer at the bottom of the BOX floor sealed, the floor impact sound level was reduced by 5 dB in the 63-Hz band compared to the bare surface.