NOVELTY - A hydrogen production system consists of an ammonia decomposition zone (2), an ammonia oxidizing zone, and a valve mechanism. The ammonia decomposition zone decomposes ammonia in the presence of a catalyst and manufactures hydrogen. The ammonia oxidizing zone oxidizes ammonia in the presence of a catalyst. The valve mechanism reverses the gas flow direction. The ammonia oxidation catalyst contains catalytically active metal supported by a support consisting of metal oxide in which oxidation reduction is possible.    USE - Hydrogen production system is used for supplying hydrogen as combustion improver in ammonia engines.    ADVANTAGE - The hydrogen production system enables continuous, economical and stable production of hydrogen over a long period of time. By supplying heat produced in the upstream ammonia oxidizing zone to the downstream zone, preheating in an electric heater is not required.    DETAILED DESCRIPTION - A hydrogen production system consists of an ammonia decomposition zone, an ammonia oxidizing zone which is provided upstream and downstream of the ammonia decomposition zone, and a valve mechanism. The ammonia decomposition zone decomposes ammonia in the presence of a catalyst and manufactures hydrogen. The ammonia oxidizing zone oxidizes ammonia in the presence of a catalyst. The valve mechanism reverses the gas flow direction after stopping flow of ammonia flowing through the upstream ammonia oxidizing zone (4), ammonia decomposition zone, and downstream ammonia oxidizing zone (3) sequentially or reverse direction for preset time. The ammonia oxidation catalyst contains catalytically active metal supported by a support consisting of metal oxide in which oxidation-reduction is possible.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the hydrogen production system. (Drawing includes non-English language text)    Circulation type reactor (1)    Ammonia decomposition zone (2)    Downstream ammonia oxidizing zone (3)    Upstream ammonia oxidizing zone (4)    Valve (5)