A connector including a housing which includes terminal receiving grooves in which metal terminals are inserted and received, respectively, from one insertion opening, an upper wall closing upper sides of the terminal receiving grooves, and retaining holes formed in the upper wall in such a manner that the inside and outside of each terminal receiving groove communicate with each other through the associated retaining hole, and a flexible retaining arm, formed on and projecting from the metal terminal, is retainingly engaged in the retaining hole. In the connector, outer grooves are formed in an outer surface of the upper wall, and extend from a fitting face of the housing (for fitting in a mating connector) toward the insertion opening, and inner grooves are formed in an inner surface of the upper wall, and extend from the insertion opening toward the fitting face, and that end of each of the inner grooves close to the fitting face communicates with that end of the associated outer groove close to the insertion opening in a direction of a thickness of the upper wall, thereby forming the retaining hole.