There are provided a leaf row in which a plurality of leaf plates are arranged in the thickness direction of the row in such a way that the respective one end faces of the leaf plates are trued up and a leaf plate drive mechanism that drives each of the plurality of leaf plates in such a way that the one end face approaches or departs from a beam axis. A step of preparing an electrochemical cell. A first load has an input and has an output coupled to a second current electrode of the second transistor.