A semi-dry electrode for recording an electroencephalogram, includes an outer membrane that forms an electrode contact surface with a predetermined area contacting a scalp; an electrode body that is connected to an edge of the outer membrane and forms an internal space into which an electrolyte solution is filled; and an electrical conductor sensor that is located inside the electrode body and measures an ion current transmitted through the outer membrane. The outer membrane has a plurality of fine holes and holes that are larger than the fine holes.