PURPOSE: To open and close a cover in single operation while holding the cover at the open position of the cover by installing a bracket, a fixed bracket, a guide shaft, a shaft for a spring and the compression spring.

CONSTITUTION: A compression spring 7 pushes a guide shaft 3 against the right end of a slot 2a for the guide shaft in a fixed bracket 2 by the force of approximately 500g under the state in which a cover 30 is closed. When the cover 30 is opened by the force of approximately 500g or more, the guide shaft 3 is moved to the left along the slot 2a for the guide shaft in the fixed bracket 2. The guide shaft 3 is shifted from the right end of the slot 2a under the state in which the compression spring 7 is most compressed, the reaction of the compression spring 7 is increased gradually from approximately 500g, and the reaction of the compression spring 7 functions as assistance upward pushing the cover 30 when the guide shaft exceeds the position of the shifting. The compression spring 7 pushes the guide shaft 3 to the left end of the slot 2a by the force of approximately 5kg under the state in which the cover 30 is opened.