PURPOSE: To improve safety by positively locking a gate roof by way of installing an auxiliary spring to energize the gate roof in the closing direction at the time of closing the gate roof and in the opening direction at the time of opening the gate roof on an oscillating member in the device of a motor-lorry and others in the title.

CONSTITUTION: A gate roof 22 is connected to an operation lever 11 through an auxiliary linkage 12, a driving arm 13, an oscillating member 14 and a connecting lever 15. This oscillating member 14 is constituted of an input lever 14a and output levers 14c, 14c, and to the head end of the input lever 14a, through an offset plate 14a1, the other end of an extension spring 16 one end of which is engaged with a pin 16a of a load carrying platform panel 21 is connected. To the intermediate part of one of the output levers 14c, 14c, through an offset plate 14c1, the other end of a spring member 17a one end of which is connected to the bottom surface of a storage member 21a is connected, and the gate roof 22 is energized in its opening direction. The tension spring 16 is energized in the closing direction in the opening state of the gate roof 22 and in the opening direction in the opening state and those states are maintained.