PURPOSE: A heat-generating composite suitable for a pocket heater for instant use and capable of controlling its temperature easily, composed of a package containing iron powder and an aqueous solution of an antioxidant separately, wherein the both components are mixed together and brought into contact with oxygen to effect the heat-generation in use.

CONSTITUTION: For example, iron powder 4 and four inner bags 5 containing an aqueous solution of an antioxidant such as ferrous chloride, are placed in an outer bag 3, and vacuum-packed with a non-breathable resin film 2. In case of use, the film 2 is torn to expose the outer bag 3, and the inner bags 5 are broken by pressing with the fingers, etc. to effect the contact of the iron powder 4 and the aqueous solution 6. The uniform mixture of the components 4 and 6 generates heat in the presence of air. The weight ratio of the iron powder 4 to the aqueous solution is pref. 7W1. Addition of a small amount of an antifreezing agent such as ethylene glycol to the aqueous solution 6 enables the use of the composite in a cold district.