To lower a heat recovery temperature and raise a heat utilization characteristic in terms of the cost of a device and an operating cost or the like by recovering heat in accordance with a reaction represented by a specific expression and utilizing heat in accordance with a reaction represented by a specific expression which is reverse to the above described reaction.

A heat recovery is carried out by the decomposition reaction of methyl formate represented by 2CH3OH→HCOOCH3+H2 and heat is utilized in accordance with the composition reaction of methyl formate represented by HCOOCH3+H2-2CH3 OH which is a reverse reaction thereto. These reactions are carried out under the presence of a copper catalyst or a noble metal catalyst. Further, these reactions are carried out in a liquid phase and methanol, H2 gas and methyl formate are separated in accordance with a reaction distillation. Thus, industrial waste heat at a low temperature of, for example, not higher than 250°C, which has been conventionally used as a heat source with difficulty and steam or hot water at a high temperature of, for example, not lower than 100°C can be generated, so that it can be effectively used for various heat sources or cooling and heating in the places requiring heat of factories or cities.