To provide the heater structure of a humidifying unit to enable prevention of the occurrence of abnormal high heating, etc., and reduced in a manufacturing cost and size by omitting a fuse.

The humidifying unit feeds air heated by a heater to a humidifying rotor that has absorbed moisture from air and discharges moisture to heated air. Feeder lines 1a and 1b of a heater body 12 are twisted together and contained in a heater case 11. When the heater body 12 is heated to an abnormally high temperature, a covering is molten, conductors are brought into contact with each other for short circuit. The fuse of a main source circuit is blown by a short circuit and power feed to the heater body 12 is cut off.