1. A cover structure comprising:a base that is attached to a circuit substrate of an electric connection box on which an electrical component is mounted, the base being used as a receptacle for a cable that is to be electrically connected to the electrical component; and
a housing that houses the circuit substrate,
wherein the base is molded from an insulating material into a unitary body that has a shape including:
a bottomed tube that has an opening into which a plug of the cable is fitted;
a drainage hole that is formed in a portion of a side plate of the bottomed tube so as to extend through a bottom plate; and
a wall that stands upright so as to surround a perimeter of the drainage hole on an outer surface of the bottom plate,
a locking rod that covers a bottom plate side of the drainage hole is provided standing upright on an inner side of the housing, and
the locking rod abuts against an inner side of the wall on the outer surface of the bottom plate.