A socket which holds an IC package and is to be mounted on a circuit board is described that includes: a housing with a bottom portion, two pairs of side wall portions and an opening accommodating the IC package, contacts and holders. The bottom portion is provided with penetration holes. The two pairs of side wall portions face each other across the opening and one pair of side wall portions are provided with ribs protruding outward. The contacts are supported by the housing so as to pass through the penetration holes and are exposed on an opposite side of the opening. The holders have first support holes and are fixed to side surfaces of the housing with the ribs passing through the first support holes.