In a protective structure for a circuit board (1) that includes a casing (3) for receiving the circuit board, the casing is provided with a recess (11) for receiving a large component part protruding from the circuit board therein, and potting material (6) is filled in a space defined between the large component part and a surrounding wall of the recess. Typically, the potting material is filled in a gap between the large component part and the surrounding wall of the recess without substantially extending out of the recess. Because the large component part is not only supported by the circuit board but also by the casing via the cured potting material, the stress acting on a connection part that connects the large component part to the circuit board is minimized, and this enhances the mechanical integrity of the circuit board assembly. Because the use of the potting material is limited to the recess, the required amount of the potting material can be minimized, and this means a lower material cost and a reduced weight. Reducing the amount of the potting material means a shorter period of time required for curing it, and this improves the production efficiency of the circuit board assembly. If the protection of the component parts from intrusion of moisture is desired, protective coating may be additionally applied to the circuit board.