An opening/closing mechanism of a cover member that can easily push down the cover member by the lever member even if the force from the base member side to the cover member is increased, improving the operability of the lever member. A solution is that the lever member 17 is rotatably supported to the base member 23 by the first shaft 31, the link plate 29 is mounted to the lever member 17 by the second shaft 32, the cover member 15 is mounted to the link plate 29 by the third shaft 33, and the link plate 29 is rotated around the axis of the first shaft 31 in the direction in which the lever member 17 closes, so that the link plate 29 moves through the second shaft 32, and the link plate 29 moves, so that the cover member 15 is depressed through the third shaft 33.