To provide a closing and opening mechanism that can prevent bent components and degraded durability when limiting the operating speed of a vertically moving lid which supports a heavy load or making its operation heavy.

In an opening and closing mechanism in which the lid is opened and closed by a vertically turning motion of the lid 1 which is supported by a support shaft 2 and supports a large retreat drum 21 of the main sheet processing device and the retreat drum 21 contacts the main body of the sheet processing device, the lid 1 is connected to the support shaft 2 and the support shaft 2 is supported to a support base 3 via a torque limiter 4. Moreover, a notch (D cut) is provided at the joint of the support shaft 2 and the lid 1 and the lid is connected to the joint 5 hinged at the notch. Further, a spring energizes the lid 1 upward.