PURPOSE: To provide a heating system for generating heat by making deuterium to be occluded into a hydrogen occlusion metal in which the exothermic reaction is controlled by deciding the state of reaction system quantitatively.

CONSTITUTION: A deuterium electrolytic system is used as a heating system and heavy water added with 0.3mol/l of LiOD is used as the electrolyte 106. A Pd plate made of a hydrogen occlusion metal is used as the cathode 101 and two Pt plates are arranged, as anodes 102, on the opposite sides to the cathode 101(Pd plate). Gases(cathode: deuterium, anode: oxygen) generated from both electrodes 101, 102 are collected while being separated through a separator 103 and the quantities thereof are measured. An operating unit operates the quantity of deuterium occluded in Pd based on the measurements. An electrolytic current/voltage controller then controls the electrolytic current or voltage based on the operated quantity of deuterium such that a quantity of occlusion corresponding to a desired exothermic quantity can be obtained.