Sheet size detection device, and an automatic document feeding apparatus using the same

摘要

PROBLEM TO BE SOLVED: To provide a sheet size detecting device and an automatic document feeder using the same capable of accurately detecting a size of a sheet even when the size and a carrying speed of the sheet change. SOLUTION: A document size detecting device 80 detects a document size wherein a document detecting sensor 83 for detecting a document G scans a document G by moving in an orthogonal direction to a carrying direction of the document G. Because a scanning rate of the document detecting sensor 83 is variable, the scanning rate of the document detecting sensor 83 can be changed in response to the size and the carrying speed of the document G. Thus, detection accuracy of the size of the document G by the document detecting sensor 83 is improved and the size of the sheet can be accurately detected.