An electrical connector to which insulated conductors of a multiconductor cable are connected by insulation piercing, which includes an insulation housing having a front recess and a rear recess; a plurality of contacts arranged in the insulation housing so that their contacting sections are exposed in the front recess and their piercing sections project upwardly in the rear recess; and a guide block disposed in the rear recess and having a lateral slot in which the insulated conductors are arranged side by side at regular intervals, a plurality of vertical slots into which the piercing sections are inserted, and a deformation groove provided behind the vertical slots for securing the insulated conductors to the guide block when it is deformed.