PURPOSE: To insulate the sound of a movable 'tokonoma' by simple light-weight structure at low cost by cutting a material such as plywood in a beltlike warmer in the clearances of floor panels and floor finishing materials, arranging the cut materials in a floor joist shape at regular intervals and forming spaces among floor joist materials.

CONSTITUTION: Floor joist materials 6 are installed onto the top face of a panel 1 at regular intervals, and floor finishing materials 4 are laid on the materials 6. Rubber legs with adjusting mechanisms are mounted on the rear of the panel 1 in the same manner as a conventional movable 'tokonoma' at that time, and the floor finishing materials 4, the floor joist materials 6 and the panel 1 are integrated by nails, adhesives, etc. Sections among the floor finishing materials 4 and the panel 1 are formed in spaces with the exception of sections, where the floor joist materials 6 are set up, at that time. Accordingly, the vibrations of a heavy-floor impulse source are absorbed by the deflection of floor finishing material 4 themselvs in the same manner as the result of a conventional method of construction of a sleeper floor joist, thus inhibiting the sound of an impulsive sound to a lower floor.