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.
