A decomposition reaction apparatus for the decomposition treatment of a thermosetting resin, which comprises a reaction apparatus comprising an introduction section for introducing a resin composition containing the thermosetting resin and a solvent containing a monomer component of the thermosetting resin or a component similar to the monomer component, a decomposition reaction section for heating and pressuring the resin composition and the above solvent so as for the solvent to have a supercritical state or a subcritical state, to thereby prepare a treated and recovered product containing a recycled resin formed by the reduction of the molecular weight of the above thermosetting resin, and a discharge section for discharging the treated and recovered product. In the above reaction apparatus, the introduction of the resin composition and the solvent, the decomposition treatment of the thermosetting resin in the decomposition reaction section and the discharge of the treated and recovered product from the discharge section are all carried out continuously, and therefore, a raw material for a recycled resin composition using an industrial or general waste containing a thermosetting resin as the above resin composition can be produced continuously.