A medium supplying mechanism that supplies medium to be supplied with one end of each medium serving as a reference includes a medium supporting unit having a plurality of extendable and contractable supporting portions that are disposed in steps and that support the medium. Supporting widths and dispositions of the supporting portions of the respective steps are determined so that the supporting portions are capable of supporting the medium having the largest size among the medium with a central line in a widthwise direction of the medium having the largest size serving as a symmetry axis.