SHEET FEEDER, SHEET READER, AND IMAGE FORMATION DEVICE

PROBLEM TO BE SOLVED: To start feed of a next document at optimum timing while balancing a merit of a leading end detection means with that of a rear end detection means.SOLUTION: This sheet feeder for transporting a separately-fed document to a reading position to read the document includes: a rear end detection means Sn3 to detect the rear end of a sheet having passed through a separating/feeding means 9; a first leading end detection means Sn1 arranged away from the separating/feeding means 9 on the downstream side in the transport direction by a predetermined distance; a second leading end detection means Sn2 arranged away from a document calling means on the downstream side in the transport direction by the predetermined distance; and a control means to determine the length in the transport direction of the document while being transported from the detection results of the rear end detection means Sn3 to detect the leading end of a document as well and the second leading end detection means Sn2. In the sheet feeder, when the transported document is determined to be smaller than a specific size by the control means, the feeding of the next document on a loading means is started at earlier one out of the time of the leading end detection of the preceding document by the first leading end detection means Sn1 and the time of the rear end detection of the preceding document by the rear end detection means.