NOVELTY - The methane production apparatus (100) has a source gas introducing unit (130) that introduces source gas into a reactor (110) of a former stage most among the reactors and a communicating path (120). A cooling unit (150) cools the generated gas generated with the reactor of the former stage more than the temperature that the methanation reaction starts, and to less than the temperature that the methanation reaction stops. The source gas introducing unit introduces water vapor into the reactor of the foremost stage with the source gas.    USE - Apparatus for manufacturing methane by making hydrogen and carbon dioxide into source gas.    ADVANTAGE - Methane is manufactured highly efficient. The thermal capacity in each reactor is increased. The per unit time temperature rise of the reaction zone in each reactor by introducing water vapor is suppressed. The methane content rate in the generated gas finally generated is improved. The situation where the catalyst deteriorates is avoided.    DETAILED DESCRIPTION - The quantity of the water vapor which the source gas introducing unit introduces is 1.2 times or less with respect to the total amount of the source gas larger than 0 time. A gas composition measurement unit (170) measures a composition of the generated gas most sent from the latter reactor among the reactors. A central control unit (180) controls the water vapor volume which the source gas introducing unit introduces so that the amount of manufacture of the methane increases, based on the result depended on the gas composition measurement unit. The number of stages of the reactor is five or less. A water removal unit which removes water from the generated gas cooled by the cooling unit is provided among the communicating paths, between the cooling unit and the latter reactor.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the methane production apparatus. (Drawing includes non-English language text)    Methane production apparatus (100)    Reactor (110)    Communicating path (120)    Gas introducing unit (130)    Cooling unit (150)    Gas composition measurement unit (170)    Central control unit (180)