<p>A weight moving in the height direction in linkage with the development and retraction of a slide guide frame is provided. The weight brakes the retraction of the slide guide frame by increase of its potential energy and promotes the development of the slide guide frame by decrease of its potential energy to reduce an operation force, and whereby a slide bar can be lightly operated and the sliding speed of the slide bar during the opening can be reduced so as to improve the safety.</p>
