PURPOSE: To detect half fitting at an early stage.

CONSTITUTION: A locking arm 13 is formed on the side of a female connector 10, an engaging groove 23 is formed on the side of a male connector 20, a short metal fixture 41 is arranged on the lower surface of the locking arm 13, and a detection terminal 42 is inserted into the lower part of the locking arm 13. When the locking arm 13 is bent halfway the fitting, the short metal fixture 41 is driven downward to produce conductive state between the short metal fixture 41 and the detection terminal 42, and when an engaging projection 13c of the locking arm 13 is inserted into the engaging groove 23 for normal fitting, non-conductive state is produced between them. By noticing half-insertion, the completion of fitting work is judged at an early stage.