To provide a bathtub with draining capability in a flange part, capable of providing the sense of expansion in the opening face by rising of the water level, allowing a user to take a bath safely in a stable posture if the user puts hands or buttocks on the flange part when entering/going out of the bathtub, and securing a wide contact area with a bathtub lid without deteriorating the function of the bathtub lid to keep the bath warm.

The bathtub is in the shape of a rectangle from the flat plane view, with the flange part 1 on top formed to slope downward toward a hot-water reservoir part 2. The inclination of at least one of short-side flange parts 3 is larger than that of a longitudinal flange part 4. The longitudinal flange part 4 is formed to gently slope.