In the case where the electrolyte membrane localized drying occurs, it provides a technique of improving the estimation accuracy of the water content of the fuel cell.
In the fuel cell system, the water content estimation unit, during the after the first condition corresponding to the electrolyte membrane localized drying is established, until the second condition corresponding to dissolution of the electrolyte membrane localized drying be established, of the fuel cell in place of the first functional amount estimate processing for estimating the moisture content of the fuel cell on the basis of the impedance on the basis of the output current value and execute the second water content estimation processing of estimating the water content of the fuel cell, the first condition, the oxidizing gas stoichiometric ratio is not less than a predetermined threshold, and will have passed the first lapse time after being above a predetermined threshold, the second condition, the output current accumulated value is the integrated value of the first to the second elapsed time from the time when the first condition is satisfied of not less than a threshold value, or an oxidizing gas stoichiometric ratio is less than a predetermined threshold, one would also passed a third time elapsed after being less than a predetermined threshold.