To provide a medium processor and a medium processing method, capable of preventing deformation or a jam of a processing target medium by reducing resistance when the processing target medium is discharged.

This medium processor 1 performing prescribed processing to the processing target medium 10 has: an insertion/discharge port 11 inserted and discharged with the processing target medium 10; a carrying means 12 carrying the processing target medium 10 to a first direction and the opposite direction to the first direction along a prescribed path continuing to the insertion/discharge port 11; a printing part 17 as a medium processing means performing prescribed processing to the processing medium 10, provided along the path; and a set guide part 25 movable between a first state that it is disposed inside a passage area S through which the processing target medium 10 passes to restrict a position in a direction crossing the first direction of the processing target medium 10 and a second state that evacuation to an outer direction of the passage area S compared to the first state is performed to release the restriction, coming into the first state in time of the carry-in when the processing target medium 10 is carried in, and coming into the second state in time of carry-out when the processing target medium is carried out.