PURPOSE: To make quick adjustment of interior temperature possible by arranging grid-shaped support members on the inside of wooden frames that are fixed to a wooden board, and by providing metal sheet so that it is fitted into grooves that run over the surface of the support members and is laid to cover the surface of the support members and the wooden frames.

CONSTITUTION: Grid-shaped support members 4 are arranged over a wooden board 2 surrounded with wooden frames 3 that are fixed to the wooden board 2 so that each one of blocks of the grid-shaped support members penetrate the wooden board 2 at right angles. A plurality of grooves 5 are provided so that the grooves extend, running over the surface of the support members 4, from one of edges of the wooden frames 3 to the opposite edge of the wooden frame. Then a metal sheet 6 that fits into the grooves and covers the surface of the support members 4 and the wooden frames 3 that adjoin the support members is provided. Hot water pipes 9 are then laid in the grooves formed by the metal sheet 6, and a plywood 7 is laid thereon, and floor finishing is made by laying carpet 8 or the like over the plywood. Thereby temperature adjustment in a room can be made, responding quickly to variations of the outside temperature by making the temperature of the metal sheet 6 quickly rise and fall.