A method for manufacturing an electrochemical device includes the following steps: a step of preparing a positive electrode, the positive electrode including a first current collector and a positive electrode layer containing a conductive polymer; a step of preparing a negative electrode, the negative electrode including a second current collector and a negative electrode layer; and a step of sealing the positive electrode, the negative electrode, and an electrolytic solution in an exterior body. The step of preparing the positive electrode includes a step of holding the positive electrode in depressurized atmosphere and then introducing gas containing CO2 as a primary component into the depressurized atmosphere.