A separator unit inserted into a fuel cell having an electrolyte layer interposed between a fuel electrode and an oxygen electrode is provided with a plate like separator that separates fuel gas supplied to the fuel electrode from oxidizing gas supplied to the oxygen electrode, and a mesh like collector having an opening that forms one of a passage through which the fuel gas flows and a passage through which the oxidizing gas flows. The collector is provided to at least one side of the separator base in abutment against one of the fuel electrode and the oxygen electrode. The separator base has a coolant passage formed therein, through which a coolant is allowed to flow, and an electrode abutment portion of the collector, which abuts against one of the fuel electrode and the oxygen electrode, has an aperture ratio higher than those of other portions of the collector.