A medium processor, for processing a thin sheet medium such as a check or bill made of paper, comprising: a transfer path through which a sheet medium may be transferred; a transfer means (20A to 20D, 22A to 22D) for transferring the medium; and an evacuation path, connected to the transfer path, for evacuating the medium out of the transfer path, at least in a certain case; wherein a datum surface for transfer motion, providing a datum position in the medium-width-wise direction for the medium during its transfer motion, is formed at an end in the medium-width-wise direction of the transfer path, perpendicular to a transfer direction of the medium; and wherein the transfer means includes a transfer roller (20A to 20D) positioned in the transfer path for transferring the medium, and an opposing roller (22A to 22D) placed so as to oppose to the transfer roller (20A to 20D) and biased against the transfer roller (20A to 20D); characterized in that a guide is provided; at least one pad roller is coaxially fixed to a turning shaft; a first end of the turning shaft is supported by a first bearing unit so as to be rotatable; a second end of the turning shaft is supported by a second bearing unit so as to be rotatable; the first bearing unit is located at a side of the datum surface for transfer motion, while the second bearing unit is located at an opposite side from the datum surface for transfer motion; the first bearing unit and the second bearing unit are fixed to a bearing unit fixing part formed in the guide; two first shaft support parts are formed in the first bearing unit so as to support the turning shaft in the medium transfer direction; two second shaft support parts are formed in the second bearing unit so as to support the turning shaft in the medium transfer direction; a space between the two first shaft support parts in the medium transfer dircection is almost the same as or a little larger than a diameter of the turning shaft; a space between the two second shaft support parts in the medium transfer direction is larger than the diameter of the turning shaft; and the transfer means (20A to 20D, 22A to 22D) is adapted to reciprocate the medium internally by using the evacuation path for shifting the medium toward the datum surface for transfer motion. a transfer path through which a sheet medium may be transferred; a transfer means (20A to 20D, 22A to 22D) for transferring the medium; and an evacuation path, connected to the transfer path, for evacuating the medium out of the transfer path, at least in a certain case; wherein a datum surface for transfer motion, providing a datum position in the medium-width-wise direction for the medium during its transfer motion, is formed at an end in the medium-width-wise direction of the transfer path, perpendicular to a transfer direction of the medium; and wherein the transfer means includes a transfer roller (20A to 20D) positioned in the transfer path for transferring the medium, and an opposing roller (22A to 22D) placed so as to oppose to the transfer roller (20A to 20D) and biased against the transfer roller (20A to 20D); characterized in that the transfer means (20A to 20D, 22A to 22D) is adapted to reciprocate the medium internally by using the evacuation path for shifting the medium toward the datum surface for transfer motion.