There is provided a control system of a chemical heat accumulator which enables to facilitate small-sizing of the chemical heat accumulator by carrying out heat release and heat accumulation according to a degree of priority by appropriately selecting a location of carrying out the heat release and heat accumulation on priority basis. A chemical heat accumulator includes a valve mechanism which makes a plurality of reactors communicate separately with a reservoir, and cuts off the plurality of reactors from the reservoir. When both reactors are in a state in which an exothermic reaction between a reaction material and a reaction medium is possible, or in a state in which an endothermic reaction in which the reaction medium is desorbed is possible, a controller which controls an opening of a valve mechanism controls the opening of the valve mechanism such that a flow rate of the reaction medium circulated between the first reactor and the reservoir for which a degree of priority of heat release or heat accumulation is high becomes higher than a flow rate of the reaction medium circulated between the second reactor and the reservoir for which the degree of priority of heat release or heat accumulation is low.