A connector comprising: an external housing including a plurality of cavities (11, 12, 13); and a plurality of internal housings (3,4,5) to be respectively inserted into the plurality of cavities (11, 12, 13), each internal housing accommodating a plurality of terminals, wherein a retainer extending in a housing insertion direction of inserting each of the internal housings (3,4,5) into each of the cavities (11, 12, 13) is formed on an inner wall surface of each of the cavities (11, 12, 13), a groove part for receiving the retainer when each of the internal housings (3,4,5) is inserted into each of the cavities (11, 12, 13) is formed on an outer wall surface of each of the internal housings (3,4,5), when each of the internal housings (3,4,5) is inserted into each of the cavities (11, 12, 13), the retainer is inserted into the groove part, and thereby the plurality of terminals accommodated in each of the internal housings (3,4,5) are secondarily locked by the retainer (31,32,34,37), characterized in that: the retainers (31,32,34,37) of the plurality of cavities (11, 12, 13) have different shapes from one another so that it prevents each internal housing (3,4,5) from being inserted into a cavity (11,12,13) different from a corresponding cavity (11,12,13) when inserting the plurality of internal housings (3,4,5) into the plurality of cavities (11, 12, 13) formed in the external housing, and the groove parts of the plurality of internal housings (3,4,5) have shapes complementary to the shapes of the retainers (31,32,34,37) of corresponding cavities (11, 12, 13). an external housing including a plurality of cavities (11, 12, 13); and a plurality of internal housings (3,4,5) to be respectively inserted into the plurality of cavities (11, 12, 13), each internal housing accommodating a plurality of terminals, wherein a retainer extending in a housing insertion direction of inserting each of the internal housings (3,4,5) into each of the cavities (11, 12, 13) is formed on an inner wall surface of each of the cavities (11, 12, 13), a groove part for receiving the retainer when each of the internal housings (3,4,5) is inserted into each of the cavities (11, 12, 13) is formed on an outer wall surface of each of the internal housings (3,4,5), when each of the internal housings (3,4,5) is inserted into each of the cavities (11, 12, 13), the retainer is inserted into the groove part, and thereby the plurality of terminals accommodated in each of the internal housings (3,4,5) are secondarily locked by the retainer (31,32,34,37), characterized in that: the retainers (31,32,34,37) of the plurality of cavities (11, 12, 13) have different shapes from one another so that it prevents each internal housing (3,4,5) from being inserted into a cavity (11,12,13) different from a corresponding cavity (11,12,13) when inserting the plurality of internal housings (3,4,5) into the plurality of cavities (11, 12, 13) formed in the external housing, and the groove parts of the plurality of internal housings (3,4,5) have shapes complementary to the shapes of the retainers (31,32,34,37) of corresponding cavities (11, 12, 13). the retainers (31,32,34,37) of the plurality of cavities (11, 12, 13) have different shapes from one another so that it prevents each internal housing (3,4,5) from being inserted into a cavity (11,12,13) different from a corresponding cavity (11,12,13) when inserting the plurality of internal housings (3,4,5) into the plurality of cavities (11, 12, 13) formed in the external housing, and the groove parts of the plurality of internal housings (3,4,5) have shapes complementary to the shapes of the retainers (31,32,34,37) of corresponding cavities (11, 12, 13).