Apparatus for opening and closing wing door of truck

An apparatus for opening and closing a wing door which is hinged to a vehicle body of a motor vehicle, the vehicle body having a frame, said apparatus being accommodated in a space defined by the frame when the wing door is closed, characterized in that said apparatus comprises

• a first arm which is pivotally mounted on the vehicle body so as to pivotally move in association with the opening and closing of the wing door;
• a second arm which is swingably linked between one end of said first arm and the wing door;
• a spring having one end which is supported relative to the vehicle body for generating a biasing force to lift up the wing door;
• a spring rod which is connected to the other end of said spring so as to move in association with the extension and retraction of said spring;
• a third arm which is swingably linked between the other end of said first arm and said spring rod;
• and
• a guide to guide said spring rod or a link point between said spring rod and said third arm for moving said spring rod in a direction which is substantially parallel with an axis of said spring.