Disclosed is a reactor including: a first reaction part and a second reaction part each comprising a reaction channel where a reactant flows, in which the reactant is applied to cause a reaction of the reactant, and which are arranged to form a gap therebetween; a heat insulating container covering at least entirety of the first reaction part, the second reaction part and the gap, in which a pressure within an inner space of the heat insulating container including the gap is lower than atmospheric pressure; and at least one getter material disposed in a space including the gap in the inner space. The getter material improves degree of vacuum in the inner space of the heat insulating container, and is disposed at the gap between the first reaction part and the second reaction part so as not to increase the size of the reactor.