PURPOSE: To provide such a lance inferiority detection method and its structure that can easily detect an inferior lance in inserting a terminal into a connector housing.

CONSTITUTION: In a lance inferiority detection structure 25, when a beak part 5 of the tip of a lance 21 is nicked due to molding inferiority, deformation of the lance 21 due to the tip of a terminal 9 is not generated. An insertion prevention face 23c of the side beak 23 rear edge on the lance 21 side face which is provided in such a relation position as interfering with an locking piece 17 formed in the terminal 9 abuts on the front edge 17a of the locking piece 17. Insertion of the terminal 9 into a terminal storage chamber 1 is thus blocked so as to be prevented from being in a pseudo-locking stage and to be an apparent uninserted state so that lance molding inferiority can be easily detected.