An opening structure includes a lower door having an upper end configured to be rotated and opened with respect to a lower surface of a vehicle body, a garnish unit located on a surface of the lower door, at least a portion of a lower end of the garnish unit configured to be tilted from the lower door, a driving unit extending in a longitudinal direction and configured to apply driving force to the lower door and the garnish unit, a first driver configured to tilt the garnish unit, a second driver configured to integrally pop up the tilted garnish unit and the lower door and to apply opening force thereto, and a hinge arm connecting the first driver and the second driver to each other.