An electroencephalogram electrode includes: a bottom portion on which a connection member is placed, the connection member which is configured to supply a biological signal that is acquired from a subject through conductive gel, to an external apparatus; an annular wall which annularly extends from the bottom portion in a contact direction with respect to the subject; and a plurality of barb members which are disposed in a holding space for the conductive gel that is located inside the annular wall, and which elongate from the bottom portion in the contact direction with respect to the subject.