A printing medium feeding apparatus comprising: a feeding part which feeds a printing medium; and a printing medium aligning roller part which is operable to align a leading edge (Pf) of the printing medium fed from the feeding part to and transfer the aligned printing medium to an image forming part, which is operable to form an image on the printing medium, wherein the printing medium aligning roller part comprises: a pair of rollers (241,243), which are adapted to transfer the printing medium to the image forming part, and an aligning shutter, which is rotationally coupled to one of the pair of the rollers (241,243), is adapted to rotate according to whether the printing medium contacts the aligning shutter with a pressure greater than a reference pressure in a reference direction, and is adapted to guide the leading edge (Pf) of the printing medium fed from the feeding part toward the reference direction, wherein the feeding part comprises a plurality of feeding cassettes (210,220,230) which feed the printing medium and other printing media from different directions to the printing medium aligning roller part; and the aligning shutter comprises: a shutter main body which is rotationally coupled to a rotational shaft of the roller to which the aligning shutter is rotationally coupled; a guiding surface which protrudes from one side of the shutter main body to contact the leading edge (Pf) of the printing medium and guide the leading edge (Pf) of the printing medium in the reference direction; and an elastic member which applies the reference pressure to the shutter main body so that the shutter main body rotates around the rotational shaft of the roller according to whether the pressure of the printing medium applied to the guiding surface exceeds the reference pressure; wherein the printing medium feeding apparatus further comprises: a flag disposed on the aligning shutter; and a sensor disposed in a rotational path of the flag, wherein when the aligning shutter rotates due to the printing medium contacting the aligning shutter with the pressure greater than the reference pressure, the flag rotates past the sensor to indicate that the printing medium is moving towards the image forming part, characterised in that the guiding surface has a semi-circular recessed shape so that the leading edge (Pf) of the printing medium is smoothly guided in the reference direction by the semi-circular recessed shape. a feeding part which feeds a printing medium; and a printing medium aligning roller part which is operable to align a leading edge (Pf) of the printing medium fed from the feeding part to and transfer the aligned printing medium to an image forming part, which is operable to form an image on the printing medium, wherein the printing medium aligning roller part comprises: a pair of rollers (241,243), which are adapted to transfer the printing medium to the image forming part, and an aligning shutter, which is rotationally coupled to one of the pair of the rollers (241,243), is adapted to rotate according to whether the printing medium contacts the aligning shutter with a pressure greater than a reference pressure in a reference direction, and is adapted to guide the leading edge (Pf) of the printing medium fed from the feeding part toward the reference direction, wherein the feeding part comprises a plurality of feeding cassettes (210,220,230) which feed the printing medium and other printing media from different directions to the printing medium aligning roller part; and the aligning shutter comprises: a pair of rollers (241,243), which are adapted to transfer the printing medium to the image forming part, and an aligning shutter, which is rotationally coupled to one of the pair of the rollers (241,243), is adapted to rotate according to whether the printing medium contacts the aligning shutter with a pressure greater than a reference pressure in a reference direction, and is adapted to guide the leading edge (Pf) of the printing medium fed from the feeding part toward the reference direction, the feeding part comprises a plurality of feeding cassettes (210,220,230) which feed the printing medium and other printing media from different directions to the printing medium aligning roller part; and the aligning shutter comprises: a shutter main body which is rotationally coupled to a rotational shaft of the roller to which the aligning shutter is rotationally coupled; a guiding surface which protrudes from one side of the shutter main body to contact the leading edge (Pf) of the printing medium and guide the leading edge (Pf) of the printing medium in the reference direction; and an elastic member which applies the reference pressure to the shutter main body so that the shutter main body rotates around the rotational shaft of the roller according to whether the pressure of the printing medium applied to the guiding surface exceeds the reference pressure; a flag disposed on the aligning shutter; and a sensor disposed in a rotational path of the flag, wherein when the aligning shutter rotates due to the printing medium contacting the aligning shutter with the pressure greater than the reference pressure, the flag rotates past the sensor to indicate that the printing medium is moving towards the image forming part, characterised in that the guiding surface has a semi-circular recessed shape so that the leading edge (Pf) of the printing medium is smoothly guided in the reference direction by the semi-circular recessed shape.