To simplify a locking mechanism and reduce insertion force by forming the side wall itself of a housing in the form of a cover capable of opening and closing instead of a retainer.

A housing 10 has a terminal fitting housing 11 in which a terminal fitting 20 is surrounded and housed. A cover-shaped side wall 15 is formed by cutting out part of a side wall so as to be capable of opening and closing. A projection 15a serving as terminal fitting locking structure to be locked in the inside terminal fitting 20 is formed on the opening/closing tip side, projections 15b, 15b are formed on the side surface so as to be capable of opening with a jig 30. When the terminal fitting 20 is housed, the cover-shaped side wall 15 is floated up with the jig 30, and a jetty 15a is shunted from the terminal fitting housing 11. After the terminal fitting 20 is housed, the cover 1 shaped side wall 15 is returned and locked with the jetty 15a. By this constitution, the locking mechanism other than a lance is obtained without the use of a separate retainer.