An opening, through which a connection section between a drive arm and a rod of a power
back door enters and exits, is covered with cover members to improve external appearance, and interference between the connection section and the cover members is eliminated when the connection section passes through the opening to prevent abnormal
noise and damage to the cover members during the passage of the connection section. A pair of cover members 6a and 6b are provided along right and left vertical edges of a vertically long opening 50 that is formed in a side edge defining a door opening 1, through which a connection section S between a drive arm 3 and a rod 4 of a power
back door for automatically driving a
back door 2 adapted to close and open the door opening 1 can enter and exit, such that lip-shaped end edges thereof face and contact each other. The cover members 6a and 6b are gradually expanded in width so that they have a greater width on the lower side thereof, and a contacting position is shifted downwardly and inwardly of the opening 50, thereby forming an entrance / exit opening 64 surrounded by lower edges of expanded sections of the cover members 6a and 6b, through which the connection section S enters and exits.