PURPOSE: To suppress vaporization of electrolyte on an electrode side and increase life of a fuel cell by installing phosphoric acid vapor supply means on the reaction material supply side of a manifold which is installed in the side of a cell stack of unit cells.

CONSTITUTION: A phosphoric acid vapor generator 14 is set on the way of a reaction material supply pipe near a supply manifold 6 of the reaction material supply side of a cell stack 2. When phosphoric acid type fuel cell is operated, phosphoric acid 16 in a closed chamber 17 is heated with a heater 18 to vaporize. The vapor is supplied from the inlet of the supply manifold 6 to the cell stack 2 with a reaction material 5. Vaporization of phosphoric acid electrolyte 10 of the cell stack 2 is suppressed by vapor pressure of phosphate. Consequently, ions between electrodes flow smoothly and desired output of electricity is maintained.