PURPOSE: To eliminate the collision noise of an operation part cover and to prevent the cover from floating by bouncing by enabling stalling operation almost at the start and end of opening/closing operation by a tension spring and an air damper.

CONSTITUTION: This device is equipped with the tension spring 10, a spring moving part 6 which is fixed at one end to a lid body 2 and holds one end of the tension spring 10 at the other end, the air damper 7 which is fixed having one end engaged with the other end of the spring moving part 6 and rotates so that the opening/closing speed of the lid body 2 is reduced nearby the start position and end position of the opening/closing operation of the lid body 2, and an attraction part 12 which inhibits the lid body 2 from operating in the opening direction. When the lid body 2 is opened or closed with a strong force, the air damper 11 reduces the opening/closing speed of the lid body 2 nearby the start position and end position of the opening/closing operation while the tension spring 10 reduces the gravitational force of the lid body 2. Consequently, the collision noise generated when part of the spring moving part 6 strikes on the attraction part 12 at the end position is reduced and the bouncing is eliminated, so that the opening end position can easily be judged.