To provide a wooden rail removably fitted in the floor of an opening part for kotatsu (foot warmer) in a state to be positioned flush with the upper surface of a floor, use the wooden rail as the support frame of a cover plate during no use of the foot warmer, and form a floor cover, closing the opening for the foot warmer, to realize an integral feeling with a peripheral floor.

An opening part 2 for a kotatsu (foot warmer) 1 is formed in the floor of a western style room, and a wooden rail 4 is removably fitted in a wooden floor 3 of the periphery of the opening 2 for the foot warmer 1 in a state to be positioned approximately flush with the upper surface of the wooden floor 3. At least one of four rail materials 5 of which the rail 4 consists is disassemble. A groove 7 is formed in an inside flank 6 of each rail material 5 of which the rail 4 is formed, and by fitting a wooden cover plate in the groove 7, a floor cover to close the opening part 2 is provided.