A medium feeding apparatus comprising: a medium placing unit on which a medium can be placed; a feeding roller configured to feed the medium from the medium placing unit; a separation roller configured to nip the medium between the separation roller and the feeding roller to separate the medium and to which a driving torque can be applied by a driving source in a second rotation direction that is opposite to a first rotation direction in which the medium is fed to a downstream side; a torque limiter configured to cause the separation roller to idle in the first rotation direction when a rotational torque applied to the separation roller in the first rotation direction exceeds a limit torque that is a predetermined upper torque limit; a torque changing unit configured to change the limit torque; a speed changing unit configured to change a rotational speed of the driving source; a load changing unit configured to change a pressing load of the separation roller against the feeding roller; and a power transmission mechanism configured to transmit power from the driving source, wherein separation setting including the pressing load, the rotational speed and the limit torque is changeable according to conditions during feeding, and characterized in that: the power transmission mechanism includes a first gear provided integrally with a rotary shaft of the separation roller, a second gear provided integrally with the rotary shaft of the separation roller and having a reduction ratio that is different from a reduction ratio of the first gear, and a switching gear displaceable between a first position where the power of the driving source is transmitted to the first gear and a second position where the power of the driving source is transmitted to the second gear, and the load changing unit is configured to switch the switching gear between the first position and the second position to change the pressing load. a medium placing unit on which a medium can be placed; a feeding roller configured to feed the medium from the medium placing unit; a separation roller configured to nip the medium between the separation roller and the feeding roller to separate the medium and to which a driving torque can be applied by a driving source in a second rotation direction that is opposite to a first rotation direction in which the medium is fed to a downstream side; a torque limiter configured to cause the separation roller to idle in the first rotation direction when a rotational torque applied to the separation roller in the first rotation direction exceeds a limit torque that is a predetermined upper torque limit; a torque changing unit configured to change the limit torque; a speed changing unit configured to change a rotational speed of the driving source; a load changing unit configured to change a pressing load of the separation roller against the feeding roller; and a power transmission mechanism configured to transmit power from the driving source, wherein separation setting including the pressing load, the rotational speed and the limit torque is changeable according to conditions during feeding, and characterized in that: the power transmission mechanism includes a first gear provided integrally with a rotary shaft of the separation roller, a second gear provided integrally with the rotary shaft of the separation roller and having a reduction ratio that is different from a reduction ratio of the first gear, and a switching gear displaceable between a first position where the power of the driving source is transmitted to the first gear and a second position where the power of the driving source is transmitted to the second gear, and the load changing unit is configured to switch the switching gear between the first position and the second position to change the pressing load. the power transmission mechanism includes a first gear provided integrally with a rotary shaft of the separation roller, a second gear provided integrally with the rotary shaft of the separation roller and having a reduction ratio that is different from a reduction ratio of the first gear, and a switching gear displaceable between a first position where the power of the driving source is transmitted to the first gear and a second position where the power of the driving source is transmitted to the second gear, and the load changing unit is configured to switch the switching gear between the first position and the second position to change the pressing load.