In a cap for an optical connector, light-receiving/emitting modules are inserted in a housing body, and the cap is attached to the housing body, so that the light-receiving/emitting modules are fixed by the cap. Protuberances are formed on the cap, and project in an attaching direction so as to be abutted against the light-receiving/emitting modules to prevent the light-receiving/emitting modules from being displaced out of position. The protuberances have elasticity. Opposite ends of each of the protuberances may be cut off at an acute angle, so that a distal end of the protuberance is substantially pointed. Alternatively, each of the protuberances is longitudinally cut into a half.