To provide a mixing device for a tub capable of minimizing the amount of bubbles generated by a mixed liquid in a tub.

The mixing device for a tub includes: a first mixing chamber 10 having supply pipes 220 through which mixed liquid is supplied, used to store mixed liquid at the bottom, and having a first internal pressure maintained at a level higher than the atmospheric pressure; a second mixing chamber 20 having supply pipes 220 through which mixed liquid is supplied, used to store mixed liquid at the bottom, and having a second internal pressure maintained at a level equal to or higher than the atmospheric pressure but lower than the first pressure in the first chamber; and a mixed liquid circulation mechanism for circulating mixed liquid in the tub 3 through the chambers in the order of the first mixing chamber 10 and second mixing chamber 20 and then returning it to the tub 3.