The invention discloses a heating device including a first cavity body, a heating member, a second cavity body, a heat conduction member, a temperature detector, and a controller. the heating member heats the fluid in the first cavity body, the fluid inlet of the second cavity body is the fluid outlet of the first cavity, the heat conduction member isolates the first cavity body and the second cavity body, the temperature detector detects the temperature of the fluid in the second cavity body, the controller performs heating control of the heating member based on the temperature detected by the temperature detector, the fluid flows into the first cavity body and then flows into the second cavity body after being heated by the heating member, and the fluid exchanges heat with the fluid in the first cavity body via the heat conduction member while passing by the second cavity body. The heating device is stable in water outlet temperature by exchanging heat of the fluid in the second cavity body before heating control with the fluid in the first cavity after the heating control; and meanwhile, the heating device is small in size because a large-size buffer water tank is not needed.