An assemble-type plate reactor was developed and its intensified heat transfer compared to that of a conventional tubular reactor in methane reforming was confirmed. This characteristic enables accurate reaction kinetic analysis because of quasi-isothermal operation with mild pressure loss. Reduced experiment cost is one of the features of the assemble-type reactor. Simple thermal design equations applicable to plate reactors were also assessed. From experiments and accurate reaction analysis using the plate reactor it is suggested that H2O and CO2 have similar reactivity for a commercial Ni/alpha-Al2O3 catalyst. The partial pressure of the oxidizing agent had much more influence on the reactivity of methane reforming than the species of this agent.