PURPOSE: To increase an adhesive area, to facilitate fixing of side walls and a bottom plate and to obviate water leakage by forming grooves at least either the step part of the inner periphery of the side walls and the outer periphery of the bottom plate.

CONSTITUTION: The wooden bathtub 10 includes the side walls 12 and the bottom plate 14 which is mounted on the side wall 12. The bottom plate 14 is mounted on the side walls 12 by step parts 16 formed on the inside wall of the side walls 12. Second grooves 52 which correspond to the first grooves 50 disposed in the step parts 6 of the side walls 12 and have a triangular sectional shape are formed on the outer periphery of the bottom plate 14. Gaps 54 are formed in the bottom of the step parts 16, i.e., between the inside wall surfaces of the side walls 12 and the outer peripheral surface of the bottom plate 14 and a synthetic resin 56 is filled therein. The synthetic resin 56 which has excellent adhesiveness, water resistance and heat resistance and has elasticity when cured is more preferable. Consequently, the expansion and contraction of the bottom plate 14 are prevented.