To provide a bathtub draining device which makes it easier to enter and exit a bathroom by reducing the height of a washing space part; allows easy maintenance as piping space can be made smaller; and prevents waste water from the bathtub from flowing back to the washing space part.

A bathtub 5 is placed above and at an interval 4 to the bathtub mounting part 2 of a bathroom floor pan 3 on which a washing space part 1 and the bathtub mounting part 2 are arranged integral with each other, and the bathtub mounting part 2 is formed to be lower than the washing space part 1 so that waste water from the washing space part 1 flows down to the bathtub mounting part 2. A first drain trap 6 where waste water flowing down from the washing space part 1 is collected for removal is provided in the bathtub mounting part 2 in such a way as to project downward. A second drain trap 8 where waste water flowed down from a drain hole 7 in the bathtub 5 is collected for removal is provided in the position of the bathtub mounting part 2 close to the first drain trap 6 in such a way as to project downward.