NOVELTY - Hydrocarbon decomposition comprises: (1) a hydrogen manufacture step where a hydrocarbon is introduced into a reactor in which a hydrocarbon decomposition catalyst is stored on which Ni, Co or Fe is supported, heating, and the hydrocarbon is decomposed to form hydrogen; and (2) a reduction step where gas containing hydrogen is introduced into a cassette containing a metal oxide and heated, and the metal oxide is reduced to a lower oxide or an element metal.    USE - Used to produce a cassette for hydrogen supply for on-site fuel cells for construction. The cassette can be used in fuel cell vehicles and hydrogen vehicles.    ADVANTAGE - A fuel cell system is obtained which is simple and low cost. The fuel is safe by occluding and releasing from the form of a metal oxide. Dangers from high pressure hydrogen containers are avoided. Hydrogen can be supplied at low cost from e.g. methane.    DETAILED DESCRIPTION - Gas exhausted from the reduction step is cycled to the hydrogen manufacture step in a closed state, and the steps (1) and (2) are repeated.    INDEPENDENT CLAIMS are also included for:    (a) a hydrogen supply method where the above cassette in which the reduced oxide or element metal is contained, is introduced with water or steam to produce hydrogen by decomposition of the water which can be supplied to devices as required;    (b) a hydrocarbon decomposition device which has a reactor containing the catalyst, a hydrogen manufacture device, a cassette for storing the metal oxide, and a reduction device for the metal oxide; and    (c) a hydrogen supply device based on the hydrocarbon decomposition device where water or steam is added to the cassette to produce hydrogen.    DESCRIPTION OF DRAWING(S) - Figure 6 shows the system (Drawing contains non-English language text).    Hydrogen Production Apparatus (1)    Cassette (2)    Heater (3)    Pipe (3a)    Pipe (3b)    Reactor (4)    Methane Inlet Pipe (5)    Heater (6)    Catalyst (7)    Gas Circulating Pump (8)    Pipe (9a)    Pipe (9b)    Metal Oxide (10)    Heater (11)    Trap for Water (12)    Filter (13)    Thermal Insulator (14)    Cover (15)    Joint (17)