A medium alignment apparatus comprising: an alignment body configured to form a transfer path for passage of a medium and to include an alignment reference surface for alignment of the medium; an alignment roller portion mounted to the alignment body to align the medium while driving the medium simultaneously; and at least one alignment sensor portion configured to detect whether the medium is aligned, detecting a position of the medium passing along the transfer path of the alignment body, wherein the alignment body comprises: a first body forming a transfer path for the medium and to which the alignment roller portion is mounted; and a second body disposed at one side of the first body to be movable relative to the first body at a speed corresponding to a transfer speed of the medium, while providing a side directed to the first body as the alignment reference surface, characterized in that the at least one alignment sensor portion is configured to detect whether the medium is aligned, by receiving and transmitting a detection signal using a prism principle, and comprises: a transmission member disposed at an outside of the alignment body providing the alignment reference surface and configured to emit the detection signal toward the alignment reference surface; and a reflection member integrally formed with the alignment body which faces the transmission member with respect to the alignment reference surface and configured to reflect the detection signal, wherein the reflection member is a prism type configured to reflect the detection signal emitted from the transmission member back to the transmission member. an alignment body configured to form a transfer path for passage of a medium and to include an alignment reference surface for alignment of the medium; an alignment roller portion mounted to the alignment body to align the medium while driving the medium simultaneously; and at least one alignment sensor portion configured to detect whether the medium is aligned, detecting a position of the medium passing along the transfer path of the alignment body, wherein the alignment body comprises: a first body forming a transfer path for the medium and to which the alignment roller portion is mounted; and a second body disposed at one side of the first body to be movable relative to the first body at a speed corresponding to a transfer speed of the medium, while providing a side directed to the first body as the alignment reference surface, characterized in that the at least one alignment sensor portion is configured to detect whether the medium is aligned, by receiving and transmitting a detection signal using a prism principle, and comprises: a transmission member disposed at an outside of the alignment body providing the alignment reference surface and configured to emit the detection signal toward the alignment reference surface; and a reflection member integrally formed with the alignment body which faces the transmission member with respect to the alignment reference surface and configured to reflect the detection signal, wherein the reflection member is a prism type configured to reflect the detection signal emitted from the transmission member back to the transmission member. a first body forming a transfer path for the medium and to which the alignment roller portion is mounted; and a second body disposed at one side of the first body to be movable relative to the first body at a speed corresponding to a transfer speed of the medium, while providing a side directed to the first body as the alignment reference surface, characterized in that the at least one alignment sensor portion is configured to detect whether the medium is aligned, by receiving and transmitting a detection signal using a prism principle, and comprises: a transmission member disposed at an outside of the alignment body providing the alignment reference surface and configured to emit the detection signal toward the alignment reference surface; and a reflection member integrally formed with the alignment body which faces the transmission member with respect to the alignment reference surface and configured to reflect the detection signal, wherein the reflection member is a prism type configured to reflect the detection signal emitted from the transmission member back to the transmission member.