To provide a continuous hot water producing technology by the heat of the submerged hydroxylation reaction of an organic material using a region of an underground supercritical water state.

A mixed fluid of water and the organic material is fed into the region of the underground supercritical or subcritical water state through a pipe line to cause the hydroxylation reaction (submerged combustion) of the organic material to produce the hot water. The combustion advances itself while keeping a supercritical state to continuously produce hot water when continuously feeding the mixed fluid of water with the organic material and an oxidant. The hot water A is used for a method of generating power or producing a resource (for example, ethanol) by the degradation of organic material.