To provide a bathtub fitting structure for a bathroom unit which eliminates the need for considering breakage and mildew resistance at seal parts, and enables an unskilled worker to surely execute works in the water- tight state.

A bathtub fitting structure of a bathroom units is so constructed that a water-tight member 5 which has compressive elasticity and breaks on receiving the force in the pulling direction is disposed in the compressed state between the back of a flange part 32 of a bathtub 3 and a set of water-tight member receiving parts 23, 25 provided in the peripheral edge part of an opening part 21 of a bathtub fitting frame 2, a wet type sealant is previously applied to one of the surfaces of the water-tight member 5 which are in contact with the back of the flange part 32 and the water-tight member receiving members 23, 25, and the other surface is made adhere to the back of the flange part 32 or the water-tight member receiving surfaces 23, 25 through an adhesive.