PURPOSE: To facilitate the fixing work of a tile backing material and improve the constructing property of the lightweight tile backing material by forming the tile backing material into a plate shape with a resin foam body, and sticking and fitting the tile backing material on the outer face of a bathtub.

CONSTITUTION: A tile backing material 1 is formed into a slender plate shape with foaming resin such as foam polystyrene forming 20 times, and recesses 2 for storing pipes are recessed along the longitudinal direction on its back face side. Vertical cut grooves 8 are provided on the end sections of the back face so that the tile backing material 1 can be cut at the length corresponding to the width size of a bathtub 3, and coupling sections 9 for connection are recessed. For the finish construction around a portion of the bathtub 3 protruded upward from a wash place 7, the tile backing material 1 can be stuck and fixed on the outer face of the portion of the bathtub 3 protruded upward with an adhesive. Even if pipes 11 exist on the outer face of the bathtub 3, they are stored in the recesses 2 of the tile backing material 1, thus the pipes 11 become no hindrance, and the tile backing material 1 can be fitted.