Abstract: A humidifier includes a water receiving chamber enclosed by a main body and a bottom plate, the water receiving chamber is divided into a gastight liquid reservoir chamber and a heating chamber communicated with exterior environment by a vertically disposed partition plate. A passage for communicating the liquid reservoir chamber and the heating chamber is disposed adjacent to the bottom plate. A baffle extending toward the bottom plate from a top wall of the main body is disposed in the heating chamber, there is a gap between the baffle and each of a circumferential sidewall of the heating chamber and a level of liquid in the heating chamber. A circumferential sidewall of the baffle, the partition plate and the top wall collectively form a backflow tank. When the humidifier and a respirator including the humidifier are tilted, the water inside the humidifier does not flow out.