To provide a floor device enabling an elongate specific piece of flooring to be replaced singly and independently of other pieces of flooring.

Locking pieces 3 each having an L-shaped cross section and consisting of vertical and horizontal pieces 3a and 3b are arranged on the lower surface of flooring 1 in longitudinally parallel relationship as they are spaced apart by a width equal to the interval between joists 2 and 2 which support the flooring 1. The horizontal piece 3b of each locking piece 3 is engaged into a receiving groove 7 cut in one side of the joist 2 along the longitudinal direction of the joist. The vertical piece 3a of the appropriate locking piece 3 is fastened to the joist 2 by a fastening screw 13 engaged through the vertical piece 3a.