The object is to provide a mixing valve and a mixing device which can more easily control the flow rates of one fluid and another fluid or fluids in comparison with a conventional mixing valve. In a mixing valve 10A in which a main passage 13 through which one fluid f1 passes and at least one subsidiary passage 14 (14A, 14B) through which the other fluids f2, f3 pass are connected via opening/closing valve portions 20A, 20B to open/close communicating openings 18A, 18B, pressure sensors 31, 32, 33 (34) are disposed in the main passage and the subsidiary passages, respectively, to detect the pressures of the fluids passing through the main passage and the subsidiary passages.