To easily and economically advantageously provide an expansion preventing floor material preventing expansion caused by moisture absorption, causing neither clearance nor warp and having excellent dimensional stability.

In the floor material with a decorative sheet 4 stuck to the surface of a wooden base material 1, recessed grooves 11, 13 are provided on the back face of the wooden base material 1, over the whole length on both end inner sides in the length direction, and recessed grooves 12, 14 are also provided over the whole length on both end inner sides in the width direction. An adhesive 5 is then filled in the four recessed grooves 11, 12, 13, 14.