To improve the use convenience by facilitating the loading of a recording medium to a tray.

This mechanism is provided with a mechanical chassis 3 equipped with a loading part 27 for loading a recording medium 100 and a tray 41 to be moved relatively to the mechanical chassis for loading the recording medium and while defining a loading position, where the recording medium is loaded on the loading part, as a reference, the tray is moved between first and second loading positions located mutually oppositely on both the sides of the loading position.