To provide a hot spring apparatus to achieve an artificial hot spring by a simple apparatus which is the most suitable for a small bathtub and by a simple controlling means.

The artificial hot spring apparatus is constituted of the bathtub 11 with a certain size, a water supply section 4 with the constant discharge rate equipped with an opening and closing valve mechanism 42 which is controlled to be opened and closed in a prescribed condition, a circulation section 2 composed of a circulation system to suck the bathing hot water B from the bathtub and to return the hot water to the bathtub which is equipped with a circulation pump 23 with the regular constant rate and a circulation water warming section (a warming tank 24) and is attached by a concentration sensor 26 of a medical fluid ingredient, and a medical fluid supplying section 3 composed of a medical fluid tank 31 and a medical fluid pump 32 to supply the medical fluid with the constant discharge rate to an installation position of the concentration sensor of the above circulation system, wherein the controlling means is adopted to actuate the circulation pump 23 when the opening and closing valve is opened and to determine whether the medical fluid pump 32 is actuated or not on the basis of the detection result of the concentration sensor.