A medium loading device comprising: a support unit that has medium holding portions which are mountable on both end portions of a roll medium formed by winding a lengthy medium into a roll shape so as to be integrally rotatable with the roll medium; and a loading portion in which the roll medium mounted with the support unit is loadable, wherein the loading portion includes: a rotary driving portion as a driving source to rotate the roll medium; and a torque transmission portion to transmit a torque of the rotary driving portion to the roll medium via the medium holding portion, characterized in that: the support unit further comprises a medium support portion to rotatably support the medium holding portion; the loading portion further comprises an operation portion that moves the torque transmission portion between a transmission position to transmit the torque to the roll medium via the medium holding portion and a non-transmission position not to transmit the torque to the roll medium via the medium holding portion, and in an axial direction of the roll medium when the roll medium is loaded into the loading portion, the operation portion is disposed between the position where the medium holding portion is located when the roll medium is loaded and the rotary driving portion. a support unit that has medium holding portions which are mountable on both end portions of a roll medium formed by winding a lengthy medium into a roll shape so as to be integrally rotatable with the roll medium; and a loading portion in which the roll medium mounted with the support unit is loadable, wherein the loading portion includes: a rotary driving portion as a driving source to rotate the roll medium; and a torque transmission portion to transmit a torque of the rotary driving portion to the roll medium via the medium holding portion, characterized in that: the support unit further comprises a medium support portion to rotatably support the medium holding portion; the loading portion further comprises an operation portion that moves the torque transmission portion between a transmission position to transmit the torque to the roll medium via the medium holding portion and a non-transmission position not to transmit the torque to the roll medium via the medium holding portion, and in an axial direction of the roll medium when the roll medium is loaded into the loading portion, the operation portion is disposed between the position where the medium holding portion is located when the roll medium is loaded and the rotary driving portion. a rotary driving portion as a driving source to rotate the roll medium; and a torque transmission portion to transmit a torque of the rotary driving portion to the roll medium via the medium holding portion, characterized in that: the support unit further comprises a medium support portion to rotatably support the medium holding portion; the loading portion further comprises an operation portion that moves the torque transmission portion between a transmission position to transmit the torque to the roll medium via the medium holding portion and a non-transmission position not to transmit the torque to the roll medium via the medium holding portion, and in an axial direction of the roll medium when the roll medium is loaded into the loading portion, the operation portion is disposed between the position where the medium holding portion is located when the roll medium is loaded and the rotary driving portion. the support unit further comprises a medium support portion to rotatably support the medium holding portion; the loading portion further comprises an operation portion that moves the torque transmission portion between a transmission position to transmit the torque to the roll medium via the medium holding portion and a non-transmission position not to transmit the torque to the roll medium via the medium holding portion, and in an axial direction of the roll medium when the roll medium is loaded into the loading portion, the operation portion is disposed between the position where the medium holding portion is located when the roll medium is loaded and the rotary driving portion.