Instantaneous water heater

An instantaneous heating apparatus is provided to minimize the delay time for hot water supply, to prevent the damage of a heating device and to discharge water at uniform temperature. An instantaneous heating apparatus(400) includes a heating portion(100) having a casing(110) provided with a space to discharge influent water through a debouchment(132) and a heating device(120) installed to the inside of the casing to heat water flowing in the casing, a housing portion(200) having a mixing space(220) within to mix the water heated by the heating portion and discharged through the debouchment to have uniform temperature distribution and an outlet(223) to discharge the water mixed at uniform temperature in the mixing space, and a pressure sensor(300) sensing the pressure of water flew in the mixing space, wherein a first temperature sensor(210) is installed to a flow passage between the debouchment of the heating portion and the mixing space of the housing portion to measure the temperature of water with increased temperature through the heating portion, a second temperature sensor(230) is installed to the lower part of the outlet of the mixing space to measure the temperature of water with uniform temperature, and a check valve(240) is installed to the lower part of the outlet of the mixing space through a check valve housing(245) to regulate the flow of water discharged from the mixing space not to flow backward and to keep the inside temperature of the instantaneous heating apparatus at atmospheric pressure when the instantaneous heating apparatus is not in use.