A sheet processing apparatus, comprising: a sheet conveyance path configured to convey a sheet having a wireless tag; and a wireless tag communication device configured to communicate with the wireless tag and including: an antenna with a plurality of radiation elements (701, 702, 703, 704) from which a polarized radio wave is emitted and including: a first radiation element extending along a first direction perpendicular to a conveyance direction of the wireless tag along the conveyance path and having a first length in the first direction, a second radiation element extending along the first direction and having a second length that is different from the first length in the first direction, a third radiation element extending along the conveyance direction and having a third length in the conveyance direction, and a fourth radiation element extending along the conveyance direction and having a fourth length that is different from the third length in the conveyance direction, and a controller configured to cause at least one of the first, second, third and, fourth radiation elements to emit a polarized wave toward the wireless tag, wherein each of the first and second radiation elements partially overlaps both the third radiation element and the fourth radiation element. a sheet conveyance path configured to convey a sheet having a wireless tag; and a wireless tag communication device configured to communicate with the wireless tag and including: an antenna with a plurality of radiation elements (701, 702, 703, 704) from which a polarized radio wave is emitted and including: a first radiation element extending along a first direction perpendicular to a conveyance direction of the wireless tag along the conveyance path and having a first length in the first direction, a second radiation element extending along the first direction and having a second length that is different from the first length in the first direction, a third radiation element extending along the conveyance direction and having a third length in the conveyance direction, and a fourth radiation element extending along the conveyance direction and having a fourth length that is different from the third length in the conveyance direction, and a controller configured to cause at least one of the first, second, third and, fourth radiation elements to emit a polarized wave toward the wireless tag, wherein each of the first and second radiation elements partially overlaps both the third radiation element and the fourth radiation element. a first radiation element extending along a first direction perpendicular to a conveyance direction of the wireless tag along the conveyance path and having a first length in the first direction, a second radiation element extending along the first direction and having a second length that is different from the first length in the first direction, a third radiation element extending along the conveyance direction and having a third length in the conveyance direction, and a fourth radiation element extending along the conveyance direction and having a fourth length that is different from the third length in the conveyance direction, and a controller configured to cause at least one of the first, second, third and, fourth radiation elements to emit a polarized wave toward the wireless tag, wherein each of the first and second radiation elements partially overlaps both the third radiation element and the fourth radiation element.