To provide a fax processing method capable of notifying a sender of the fact of the wrong transmission while being capable of judging that a back side of a facsimile sheet is transmitted without being subject to restrictions in a sheet layout structure of the facsimile sheet.

A fax processing method comprises: an analysis step for analyzing front and back information included in a facsimile data received via a transmission and reception section; a comparison step for comparing an analysis result acquired in the analysis step with back side designation information indicating that an image corresponding to the facsimile data stored in storage in advance is the back side of the facsimile sheet transmitted by the sender side; and a transmission step for transmitting the purport that the received facsimile data is the back side of the facsimile sheet transmitted by the sender side via the transmission and reception section in the case where the received facsimile data is the back side of the facsimile sheet transmitted by the sender side as a result of the comparison in the comparison step.