To humidify a space by a portable humidifier generating steam by oxidation heat of metallic powder causing oxidative reaction.

A heat generating portion metallic mixed powder 1 including metallic powder such as iron causing oxidative reaction, is coated with a water permeable heat generating portion upper coating portion 2 and an air permeable and water permeable heat generating portion lower coating portion 3, the water of proper amount is allowed to flow and penetrate into the heat generating portion upper coating portion 2 from a water outlet 6 connected with a water storage tank 4 mounted at its upper portion, the air sucked from a suction opening 7 and including oxygen, mainly enters to the heat generating portion metallic mixed powder 1 from the heat generating portion lower coating portion 3, and the water penetrating into the heat generating portion upper coating portion 2 is vaporized by oxidation heat generated in oxidizing the heat generating portion metallic mixed powder 1, and released to a space from a discharge opening 8 as steam to humidify the space. A heat generating portion lower guide 9 and a heat generating portion side guide 10 define a space absolutely necessary for allowing oxygen to sufficiently spread to the heat generating portion metallic mixed powder 1.