The invention discloses an opening-closing mechanism applied to paper medium transmission and aims to solve defects in an opening-closing mechanism of a cash circulating machine that the structure is complicated; operations are in convenient; movable parts of the opening-closing mechanism can be swayed up and down; and smoothness of paper cash transmission and paper cash recognition accuracy are influenced. The mechanism disclosed by the invention comprises a fixed frame body and a movable frame body hinged on the fixed frame body, wherein a damping hinge is connected between the movable frame body and the fixed frame body; a hook plate is disposed on the movable frame body; a reset spring is connected between the hook plate and the movable frame body; a handle is disposed on the hook plate; hinge plates are disposed on two sides of the hook plate; pressing edges are disposed on the hook plate; the pressing edges are close to the front side of the movable frame body and can be pressed against the front side of the movable frame body; limiting edges and guide edges which are disposed adjacently are set on the hinge plate; hook holes are formed in the limiting edges; a limiting pin is disposed on the fixed frame body; and the limiting pin is clamped in the hook hole.