The invention relates to a sheet conveyance device, and image forming apparatus and image reading unit including same. The objective of the invention is to reduce intervals of paper when continually conveying special sheets in a sheet conveyance direction that is slightly smaller than a predetermined length of the sheet size, and to prevent the intervals of paper increasing when conveying special sheets that is fully longer than the length of the conveyance direction. The sheet conveyance device, namely ADF (51) comprises when a sheet length detector (S4) detects that the sheet on the loading section (53) in the sheet conveyance direction is smaller than the predetermined length, and when the leading-edge of the sheet is detected by a detector including a leading-edge detector (S1; S2), or the trailing-edge of the sheet is detected by a trailing-edge detector (S3), the conveying control of the next sheet is started.