1. A medical image output system, comprising a medical image transferring apparatus for transferring received medical image data to a plurality of medical image forming apparatuses, each medical image forming apparatus outputting a sheet-like recording medium having an image formable region in which a medical image is formed based on the transferred medical image data; wherein each of the medical image forming apparatuses includes a storage unit for storing image formable region information representing the image formable region; and wherein the medical image transferring apparatus includes: an obtaining unit for obtaining the image formable region information stored in the storage unit of each of the plurality of medical image forming apparatuses; a determination unit for determining an image formation size based on the image formable region information obtained by the obtaining unit; an expansion or contraction unit for expanding or contracting the received medical image data according to the image formation size determined by the determination unit; and a transfer unit for transferring the medical image data expanded or contracted by the expansion or contraction unit to the medical image forming apparatus.