NOVELTY - A fuel cell comprises power generation units each including electrolyte electrode assemblies (a,b). The electrolyte electrode assembly (a) is stacked on a metal separator (A). A metal separator (B) is stacked on the electrolyte electrode assembly (a). The electrolyte electrode assembly (b) is stacked on the metal separator (B). A metal separator (C) is stacked on the electrolyte electrode assembly (b). The electrolyte electrode assemblies (a,b) each including a pair of electrodes and an electrolyte interposed between the electrodes.    USE - Fuel cell such as solid polymer electrolyte fuel cell is used for generating electricity.    ADVANTAGE - The fuel cell has high productivity, and is economical.    DETAILED DESCRIPTION - A fuel cell comprises power generation units each including electrolyte electrode assemblies (a,b). The electrolyte electrode assembly (a) is stacked on a metal separator (A). A metal separator (B) is stacked on the electrolyte electrode assembly (a). The electrolyte electrode assembly (b) is stacked on the metal separator (B). A metal separator (C) is stacked on the electrolyte electrode assembly (b). The electrolyte electrode assemblies (a,b) each including a pair of electrodes and an electrolyte interposed between the electrodes. Reactant gas flow fields (I-IV) are formed between the metal separator (A) and the electrolyte electrode assembly (a), between the electrolyte electrode assembly (a) and the metal separator (B), between the metal separator (B) and the electrolyte electrode assembly (b), and between the electrolyte electrode assembly (b) and the metal separator (C), respectively, for flowing a predetermined reaction gas along power generation surfaces. The reactant gas flow fields (I-IV) have several flow grooves. A coolant flow field is formed between the power generation units for flowing a coolant, where an electrode catalyst is deposited on the same area in each of the electrolyte electrode assemblies (a,b). The number of the flow grooves in the reactant gas flow field (I) for flowing one reactant gas is different from that of the flow grooves in the reactant gas flow field (III) for flowing the one reactant gas. The number of the flow grooves in the reactant gas flow field (II) for flowing another reactant gas is different from that of the flow grooves in the reactant gas flow field (IV) for flowing the other reactant gas.