PURPOSE: To provide the circulatory injection device of hot water in a bathtub, which can prevent cold water from being injected immediately after this device is operated.

CONSTITUTION: In the circulatory injection device 13 for hot water in a bathtub, which is installed outside of a bathtub 11, allows hot water 12 in the bathtub 11 to circulate and injects it together with bubbles into the bathtub 11, a branch conduit line 21 is connected to the halfway of a hot water feed conduit line 18 being a part of circulating conduit line 15 of the hot water 12, and by an operation of the circulating injecting device 13, water which remains behind in the circulating conduit line 15 is discharged to the outside of the circulating line 15 from the branch conduit line 21.