In a waterproof control unit in which a part of a connector housing mounted on a circuit board is exposed and the circuit board is hermetically housed in a casing including a base and a cover, a sealing gap between the cover and the connector housing is defined between fitting surfaces of a first concave thread and a first convex thread, and a waterproof sealing material is applied to the sealing gap. A waterproof sealing material is applied to the latter sealing gap. Each of the sealing gaps extends inward and outward across an inner boundary surface of a partition wall of the connector housing. Plane movement of each of the sealing gaps is restricted by side-surface convex threads and side-surface concave threads.