A hot-water and cold-water mixing device is provided wherein a hot-water side valve element and a cold-water side valve element are provided for regulating the respective flow rates of hot and cold water flows. The valve elements are constructed so as to possess a temperature regulating function exercised by varying the hot-water to cold-water mixing ratio depending on a biasing force, and also an automatic pressure regulating function to automatically accommodate any sudden pressure changes. The water mixing device of the foregoing construction is compact in size and is capable of adjusting the final water temperature reliably and speedily.