A humidity regulating unit including a heating element housed inside a covering that has a porous retaining wall through which water does not pass but steam or gas passes. In one embodiment, the covering has several bulges along the circumference of the heating element that protrudes outward from the outer surface of heating element to form several water routes along the outer surface of heating element. The covering and the outer surface of heating element are bonded between adjacent water routes so that the outer surface of heating element is used as part of the wall of the water routes. As a result, the size of heating element does not restrict making the cross section of each water route as small as possible, and even if the covering breaks, the amount of water leaking from the humidity regulating unit is minimized.