A method is provided that modifies a catalyst layer of a membrane catalyst layer assembly, which is manufactured by transferring the catalyst layer formed on a transfer sheet onto an electrolyte membrane. In the catalyst layer correction method, presence or absence of a defect in the catalyst layer is detected. The defect is removed based on the size and position of the detected defect. The portion from which the defect has been removed is repaired by application thereto of a correcting ink corresponding to the catalyst layer.