To provide a cover structure of a door opening/closing device which can secure the rigidity of an upper part even if a lateral cover reaches a covering position, and can improve appearance and security.

The cover structure is equipped with the door opening/closing device U which moves a slide door 4 between a closed position D1 and a protrusion position D2, and a vertical pivot end 752 pivoted to a vehicle body side around a vertical center line Lh. The cover structure includes: the lateral cover 75 which swings the door opening/closing device U in which the slide door is supported by an extension 751 extending from the vertical pivot end between the covering position K2 for laterally covering and an overlapping position K1 for overlapping with the inner wall of the slide door; a trim member 74 having a substrate 740 supported near the circumferential part of the door opening, a vertical cover end 741c extending from the substrate and arranged opposite to the vertical support end, and a trim protrusion 742 formed protruding to the outside of the vehicle at the upper part of the substrate; and an engagement projection 756 formed protruding to the extension 751 and stacked on the upward surface ft1 of the trim protrusion.