An electronic unit device includes a connector and a casing. The connector is connectable to a to-be-connected device. The casing includes a cover panel which can be opened and closed. The cover panel comprises a panel body and a partial panel. The panel body has a cut section. The partial panel is attachable and detachable to and from the cut section, and covers at least the surface of the connector, when the partial panel is attached into the cut section. The panel body includes a falling-prevention section, for preventing the installed partial panel from falling from the cut section, and a guide section for guiding the partial panel. The partial panel includes at least one engagement section to be engaged with the falling prevention section. The partial panel includes a section, to be in contact with the panel body, which is formed in such a shape as to be fit into the guide section.