The utility model discloses an instantaneous electric heating device, which comprises a shell, wherein the shell is provided with a water inlet, a water flow control system communicated with the water inlet, a heating system and a water outlet, the water inlet and the water outlet are respectively provided with a temperature detector, and the heating system is internally provided with a dry-burning-preventing protection temperature controller. On one hand, the instantaneous electric heating device can conveniently adjust and control water flow, one the other hand, the instantaneous electric heating device has a safety function of dry burning prevention; simultaneously, a silicon controlled rectifier and a constant temperature control system are also connected with the heating system of the instantaneous electric heating device, so that the temperature of outlet water is constant; and an electricity leakage coil is connected with the heating system, so that a power supply can be cut off automatically when the instantaneous electric heating device is subjected to electricity leakage, and the safety function of the instantaneous electric heating device can be further improved.