A low-cost solid polymer electrolyte fuel cell unit including a metal separator is provided. The cell unit has a structure that may have high corrosion resistance and durability. The solid polymer electrolyte fuel cell unit includes a polymer electrolyte membrane, a pair of gas-diffusible electrodes fixed at opposing surfaces of the polymer electrolyte membrane, a pair of gas-diffusible porous conductive graphite collectors fixed in contact with the outer sides of the electrodes; a pair of aluminum separators for introducing a fuel gas and an oxygen-containing gas to the electrodes separately from one another, and porous conductive buffer layers provided between the separator and the graphite collector, and having flexibility and air permeability. The separator surfaces in contact with the buffer layers are each provided with a conductive coating having a thickness in the range from 0.01 m to 20 m.