NOVELTY - A reactor (1) comprises first (4) and second reaction part (6) each containing reaction channel (8) arranged to form gap between them; a heat insulating container, covering at least entirely reaction parts and the gap; and at least one getter material disposed in space including gap in the inner space of heat insulating container. In the gap, the pressure within inner space of heat insulating container including gap is lower than atmospheric pressure.    USE - Particularly useful as a microreactor module built into electronic equipment such as a notebook personal computer, PDA, electronic organizer, digital camera, wrist watch, register, and projector for generating a hydrogen gas used for a fuel cell (from drawings).    ADVANTAGE - The reactor comprises vacuum heat insulating structure, which improves the degree of vacuum in an insulating container while the reactor is downsized. 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. The, electric power supplied to the heating wire can be reduced and the use efficiency of energy becomes higher. Thus, it is possible to start-up the reactor in comparatively short time. The getter material and wire can be heated with the heat of the low-temperature reaction part, which results superior heat efficiency. The surface area exposed outside is suppressed, and the heat release to the outside of the heat insulating package can be suppressed, and the heat loss can be suppressed. The reactor can be downsized and simple to operate. Since the partition walls which partition the channels are made relatively thin, the heat capacity of high-temperature reaction part, low-temperature reaction part, connecting pipe, supply and discharge part can be reduced and can be rapidly heated from the room temperature to high temperature in early stage of the operation. Since the external circulation pipe is coupled between low-temperature reaction part and the heat insulating package, the stress occurred in the external circulation pipe and can be reduced.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of a microreactor module 1:    reactor (1)    discharge part (2)    first reaction part (4)    second reaction part (6)    connecting pipe (8)    circulation pipe (10)    base plate. (28, 102)