A medium feeding device, comprising: a container member that accommodates sheet media; a discharging member located further than the media accommodated in the container member in a discharging direction in which the media are discharged, to discharge the media one by one; a hand-over member disposed above the container member to suck the media accommodated in the container member with air and pass the media to the discharging member; a floating device disposed on a side of the media accommodated in the container member to blow air to an upper area of a side end surface of the media to float the media while an upper portion of the media is separated; a detector that detects a separation state of the medium floated by the floating device; and a controller that controls a medium-feeding operation including a pre-feeding blowing operation and a during-feeding blowing operation, the pre-feeding blowing operation serving as an air blowing operation performed by the floating device before the medium is fed, and the during-feeding blowing operation serving as an air blowing operation performed by the floating device from a start of feeding the medium to an end of feeding the medium, wherein while performing the pre-feeding blowing operation or the during-feeding blowing operation, the controller performs detection with the detector, and on condition that a result of the detection fails to satisfy a preset target range, the controller changes a parameter for the medium-feeding operation including at least one of the pre-feeding blowing operation or the during-feeding blowing operation, the medium feeding device characterised in that after repeating detection with the detector and a change of the parameter a predetermined number of times while the during-feeding blowing operation is performed, the controller performs detection with the detector, and the controller includes a limiter that limits, on condition that a result of the detection fails to satisfy the target range, a medium feeding operation to be performed after the operation of feeding a medium that is being fed is finished. a container member that accommodates sheet media; a discharging member located further than the media accommodated in the container member in a discharging direction in which the media are discharged, to discharge the media one by one; a hand-over member disposed above the container member to suck the media accommodated in the container member with air and pass the media to the discharging member; a floating device disposed on a side of the media accommodated in the container member to blow air to an upper area of a side end surface of the media to float the media while an upper portion of the media is separated; a detector that detects a separation state of the medium floated by the floating device; and a controller that controls a medium-feeding operation including a pre-feeding blowing operation and a during-feeding blowing operation, the pre-feeding blowing operation serving as an air blowing operation performed by the floating device before the medium is fed, and the during-feeding blowing operation serving as an air blowing operation performed by the floating device from a start of feeding the medium to an end of feeding the medium, wherein while performing the pre-feeding blowing operation or the during-feeding blowing operation, the controller performs detection with the detector, and on condition that a result of the detection fails to satisfy a preset target range, the controller changes a parameter for the medium-feeding operation including at least one of the pre-feeding blowing operation or the during-feeding blowing operation, the medium feeding device characterised in that after repeating detection with the detector and a change of the parameter a predetermined number of times while the during-feeding blowing operation is performed, the controller performs detection with the detector, and the controller includes a limiter that limits, on condition that a result of the detection fails to satisfy the target range, a medium feeding operation to be performed after the operation of feeding a medium that is being fed is finished.