To enable to suppress water pyrolysis prone to progress in members constituting a fuel cell.

An operation method of a fuel cell system equipped with an electrolyte layer, catalyst electrodes arranged at either side of the electrolyte layer, and a fuel cell 15 comprises a first process of obtaining an inner temperature of the fuel cell 15, a second process of obtaining water pyrolysis critical steam pressure of materials constituting the electrolyte layer at the temperature obtained, a third process of leading out interface steam pressure expressing a degree influencing the pyrolysis in steam pressure as a value showing a state under current operating conditions of the fuel cell in a local region in the vicinity of the interface between a first electrode out of the catalyst electrodes of a side generating product water accompanying power generation and the electrolyte layer, and a fourth process of changing control of the fuel cell system 10 so that the interface steam pressure go below the water pyrolysis critical steam pressure, when the interface steam pressure exceeds the water pyrolysis critical steam pressure in controlling the fuel cell system 10 so that the fuel cell 15 generate a required power.

COPYRIGHT: (C)2007,JPO&INPIT