A reactor includes a reaction part and a removal part. The reaction part is configured to generate at least two products as a result of a reaction of an unreacted material. The removal part is configured to selectively occlude at least one product from the at least two products so as to separate and remove the at least one product. The removal part includes an absorbent and a cooling unit. The absorbent releases heat at time of the selective occlusion of the at least one product. The cooling unit is configured to remove the heat released by the absorbent.