Abstract: 35 g of a heating medium comprising 70 to 85% of powdered aluminum and 15 to 30% of powdered calcium oxide on the basis of the total weight of the heating medium is contacted with 80 ml of water to react the powdered calcium with water at a first reaction step to generate heat of reaction and calcium hydroxide, and then the calcium hydroxide is reacted at a second reaction step with powdered aluminum to generate heat of reaction to make use of approximately 3886 cal/g as the sum of the heat of reaction generated at the first reaction step and second reaction step, which can arrive at temperatures of approximately 100 ° C. for a short time which can be maintained for at least 20 minutes. The heating medium of this invention is built in a heating apparatus of a heating cooking container without increasing the weight and bulk of the container.