Reactor

A reactor comprising

• a reaction vessel having an inlet for a to-be-reformed gas and an outlet for a reformed gas,
• a pair of electrodes for plasma generation, disposed in an internal space of the reaction vessel so as to face each other,
• a power source for applying a voltage to the pair of electrodes, and
• a catalyst for promoting reforming reaction of the to-be-reformed gas,
• wherein
• one of the pair of electrodes is a linear electrode,
• the other of the pair of electrodes is a honeycomb electrode made of a conductive ceramics having a plurality of cells to act as gas passages partitioned by partition walls,
• the catalyst is loaded on the partition walls of the honeycomb electrode, and
• the honeycomb electrode has a cell density of 4 to 192 cells/cm2 and the ratio of the maximum outer diameter of each cell-opening end face of the honeycomb electrode to the length of the honeycomb electrode in the cell-extending direction is in a range of 0.50 to 1.2.