There are provided a warm water supply device and a warm water supply method, and more particularly, an instant warm water supply device and an instant warm water supply method capable of supplying warm water within a short time by controlling a flow rate. The warm water supply device includes: a heater heating water introduced therein with a heating capacity an introduction valve adjusting an amount of water introduced to the heater and a valve controller controlling a degree of opening and closing of the introduction valve by using a target water temperature and the heating capacity.
