To provide a plate supply and discharge device and a printing plate forming device which are capable of transferring plates and printing plates of various sizes and preventing the plates and printing plates from being damaged in the plate supply and discharge device (printing plate forming device). A plate supply and discharge unit (4) which supplies a plate (P1) to a drawing unit (3), receives a printing plate P2, which is obtained by drawing an image on the plate P1, from the drawing unit (3), and delivers it to a processor. The plate supply and discharge unit includes a plate supply table (41) for allowing the plate (P1) to float at atmospheric pressure, moves the plate (P1) in a state of being allowed to float at atmospheric pressure above the plate supply table (41), and supplies it to the drawing unit (3).