To more efficiently perform sheet seaming processing and sheet cutting processing.

A sheet processing device 200 includes: a conveying unit 210 to convey a sheet; first and second adjusting units 220 and 230 to stop the sheet at a predetermined position and adjust the position of the sheet; a seaming unit 240 to seam the sheet in which conveyance is stopped by the first adjusting unit 220 and which is adjusted by the first and second adjusting units 220 and 230; and a cutting unit 250 to convey the sheet which has been seamed by the seaming unit 240 and cut the margin portion of the sheet. After the completion of the sheet adjustment by the first and second adjusting units 220 and 230 and the completion of the seaming processing by the seaming unit 240, the sheet in which conveyance is stopped by the first adjusting unit 220, is conveyed to the cutting unit 250.