FUEL CELL

PROBLEM TO BE SOLVED: To provide: a fuel cell in which an initial defect during manufacturing and deterioration in an electrolyte membrane developing in a fuel cell operation environment can be precisely diagnosed; a diagnostic method of the fuel cell; and an operation method of the fuel cell.SOLUTION: A fuel cell includes a laminate in which a plurality of fuel battery unit cells having a hydrogen ion conductive polymer electrolyte membrane held by an oxidant electrode and a fuel electrode are stacked, and an electrically conductive separator having an oxidant passage and a fuel passage is inserted between the unit cells to be fastened. The laminate is obtained by stacking a unit cell that, when the hydrogen leak current of a unit cell measured in a first measuring condition is compared with the hydrogen leak current of a unit cell measured in a second measuring condition in which the moisture content of the polymer electrolyte membrane is set to be lower than that of the polymer electrolyte membrane in the first measuring condition, satisfies a relation of the hydrogen leak current measured in the second measuring condition