A plug side connector assembly forming a multi-pole connector by combining a plurality of plug side connectors that can be joined to and separated from one another, wherein each plug side connector includes a plug side housing having a substantially rectangular parallelepiped shape and having a pair of side faces (12A, 12B) that can each oppose an adjacent plug side connector, each plug side connector receiving a plug side terminal therein, and wherein the plug side housing is provided with at least one groove on one of the side faces (12A, 12B) thereof, and at least one linear protrusion on the other side face (12A, 12B) thereof in such a manner that only when a particular combination of two of the plug side connectors are adjacent to each other, the groove of one of the two plug side housings slidably engages with the linear protrusion of the other plug side housing, or the linear protrusion of one of the two plug side housings slidably engages with the groove of the other plug side housing, characterized in that the plug side housings are each provided with a through hole extending orthogonally to the side faces (12A, 12B) thereof, and the plug side connector assembly further comprises a connecting rod passed into the through holes of the plug side housings to join the plug side housings in a mutually aligned relationship, wherein the plug side terminals each consist of a female terminal received in a terminal receiving hole defined in the corresponding plug side housing, and the female terminal is provided with an engagement portion configured to be engaged by the connecting rod when the female terminal is inserted in a prescribed insertion position in the terminal receiving hole so that the connecting rod serves as a retainer for retaining the female terminal in the prescribed insertion position. wherein each plug side connector includes a plug side housing having a substantially rectangular parallelepiped shape and having a pair of side faces (12A, 12B) that can each oppose an adjacent plug side connector, each plug side connector receiving a plug side terminal therein, and wherein the plug side housing is provided with at least one groove on one of the side faces (12A, 12B) thereof, and at least one linear protrusion on the other side face (12A, 12B) thereof in such a manner that only when a particular combination of two of the plug side connectors are adjacent to each other, the groove of one of the two plug side housings slidably engages with the linear protrusion of the other plug side housing, or the linear protrusion of one of the two plug side housings slidably engages with the groove of the other plug side housing, characterized in that the plug side housings are each provided with a through hole extending orthogonally to the side faces (12A, 12B) thereof, and the plug side connector assembly further comprises a connecting rod passed into the through holes of the plug side housings to join the plug side housings in a mutually aligned relationship, wherein the plug side terminals each consist of a female terminal received in a terminal receiving hole defined in the corresponding plug side housing, and the female terminal is provided with an engagement portion configured to be engaged by the connecting rod when the female terminal is inserted in a prescribed insertion position in the terminal receiving hole so that the connecting rod serves as a retainer for retaining the female terminal in the prescribed insertion position.