A connector is provided that retains a terminal fitting when a retainer is attached to a connector housing from the side. The connector housing has a cavity into which a terminal fitting is inserted and a retainer insertion hole. The retainer is attached to the connector housing from the side through the retainer insertion hole. The retainer insertion hole extends entirely through the connector housing and penetrates from opposing outer side walls of the connector housing. The retainer is displaced between a provisional engaging position and a complete engagement position in which the terminal fitting is locked. The retainer preferably has a same height as the height between the opposing outer side walls.