A water heater comprising: a hot water tank; a heating unit which heats water in the hot water tank; and a middle temperature water outlet unit provided inside the hot water tank, wherein the middle temperature water outlet unit includes a plurality of openings (61a, 61b, 61c, 61d) through which hot water within the hot water tank flows into the middle temperature water outlet unit, a switching portion (63a, 63b) that changes an opening area of each of the plurality of openings (61a, 61b, 61c, 61d), and an extraction portion, the middle temperature water outlet unit mixes respective parts of the hot water flowing from the plurality of openings (61a, 61b, 61c, 61d) into the middle temperature water outlet unit to produce hot water having a predetermined temperature, and discharges the hot water having the predetermined temperature from the extraction portion to an outside of the middle temperature water outlet unit, and when at least two of the plurality of openings (61a, 61b, 61c, 61d) are opened, a temperature of the hot water flowing into the middle temperature water outlet unit from one of the two opened openings (61a, 61b, 61c, 61d) is different from a temperature of the hot water flowing into the middle temperature water outlet unit from another one of the two opened openings (61a, 61b, 61c, 61d), characterized in that the middle temperature water outlet unit further includes a shape memory portion that moves the switching portion (63a, 63b) based on a temperature of hot water around the shape memory portion. a hot water tank; a heating unit which heats water in the hot water tank; and a middle temperature water outlet unit provided inside the hot water tank, wherein the middle temperature water outlet unit includes a plurality of openings (61a, 61b, 61c, 61d) through which hot water within the hot water tank flows into the middle temperature water outlet unit, a switching portion (63a, 63b) that changes an opening area of each of the plurality of openings (61a, 61b, 61c, 61d), and an extraction portion, a plurality of openings (61a, 61b, 61c, 61d) through which hot water within the hot water tank flows into the middle temperature water outlet unit, a switching portion (63a, 63b) that changes an opening area of each of the plurality of openings (61a, 61b, 61c, 61d), and an extraction portion, the middle temperature water outlet unit mixes respective parts of the hot water flowing from the plurality of openings (61a, 61b, 61c, 61d) into the middle temperature water outlet unit to produce hot water having a predetermined temperature, and discharges the hot water having the predetermined temperature from the extraction portion to an outside of the middle temperature water outlet unit, and when at least two of the plurality of openings (61a, 61b, 61c, 61d) are opened, a temperature of the hot water flowing into the middle temperature water outlet unit from one of the two opened openings (61a, 61b, 61c, 61d) is different from a temperature of the hot water flowing into the middle temperature water outlet unit from another one of the two opened openings (61a, 61b, 61c, 61d), characterized in that the middle temperature water outlet unit further includes a shape memory portion that moves the switching portion (63a, 63b) based on a temperature of hot water around the shape memory portion.