A connector housing is provided to prevent a locking portion from being excessively deformed when the insufficient insertion of a terminal fitting is detected. Cavities 3 are provided in two stages in the connector housing, and locking portions 11 are arranged back to back to share deformation permitting spaces 16. The upper and lower locking portions 11 are arranged such that the longitudinal axes thereof are transversely offset to each other. Detecting portions 23 to be inserted into the deformation permitting spaces 16 project from a retainer 20. At the left and right ends of an inserting end surface 24 of each detecting portion 23, excessive deformation preventing portions 25 are formed symmetrically with respect to vertical direction. The excessive deformation preventing portions 25 can individually come into contact with leading ends 13 of the upper and lower locking portions 11. If a female terminal fitting 8 is insufficiently inserted as in the upper stage of FIG. 7, the retainer 20 may further deform the locking portion 11 after coming into contact therewith, while being inserted. However, the excessive elastic deformation of the locking portion 11 is restricted by the leading end 13 thereof being brought into contact with the excessive deformation preventing portion 25 at the lower side.