A connector housing has a lock arm for locking a terminal therein. The lock arm deflects in an complete insertion state of the terminal so that a spacer abuts against a side surface of the lock arm. The lock arm is formed with a projection which abuts the incompletely inserted terminal in the spacer advancing direction. The projection may be a plate piece elongated in the longitudinal direction of the lock to be pinched by a pair of a resilient contact plates of the terminal. Alternatively, the lock arm may have a protrusion engaging with an engagement hole formed in the connector housing. The protrusion is a rectangular plate extending from the fore end of the lock arm. An inclined guide surface continuos with the engagement hole may be provided in the connector housing. Alternatively, the connector housing may have an inner embossed wall positioned closely to the deflected lock arm to oppose to the spacer. A clearance between the embossed wall and the lock arm is determined within the elastic deflection limit of the lock arm.