A connector is mateable with a mating connector having two mating lock portions along an upper-lower direction. The connector comprises a housing and two additional members held by the housing. The housing has a projecting wall projecting upward in the upper-lower direction, an outer wall surrounding the projecting wall in a horizontal plane perpendicular to the upper-lower direction and a receiving portion which is a space formed between the outer wall and the projecting wall and partially receives the mating connector under a mated state of the connector with the mating connector. Each of the additional members has a lock portion. The two lock portions are located at opposite sides of the projecting wall, respectively, in a horizontal direction perpendicular to the upper-lower direction and face the receiving portion. Under the mated state, the lock portions lock the locked portions, respectively, to maintain the mated state.