A link mechanism capable of setting any desirable speed of opening/closing a lid during a series of the opening/closing operation and capable of exerting a strong driving force is provided. A lid (6) is attached to a lid bracket (31). The lid bracket (31) is pivotally connected to a driving lever (14) and a coupled-driving lever (15) with which the lid (6) is opened or closed. The driving lever (14) is provided with a cam having an elongated hole (34), into which a driving pin (36) provided to a sector gear (13) is fitted. The sector gear (12) is driven by a motor through a pinion (22). According to rotation of the sector gear (13), the driving pin (36) moves in the elongated hole (34) and drives the driving lever (14). Since the distance between the center of the sector gear (13) and the driving pin (36) is larger than the radius of the pinion (22), such mechanism exerts a strong driving force.