Automatic document feeder with jam determination control

An automatic document feeder comprising:

• a paper feed tray on which a plurality of originals can be placed;
• a separating unit that picks up originals one by one from the paper feed tray;
• a scanning unit that receives the originals from the separating unit and scans the originals one by one;
• a discharge tray on which the originals scanned by the scanning unit are discharged;
• an input unit with which size information indicative of a size of the originals placed on the paper feed tray is input;
• a detection unit that is arranged on a conveying path between the separating unit and the scanning unit and that detects actual size information indicative of an actual size of an original when the original is conveyed in the conveying path;
• a calculating unit that calculates a first original length from the size information and calculates a second original length from the actual size information;
• a comparing unit that compares the first original length with the second original length and outputs a result of comparison;
• a jam-determining-value setting unit that sets, when the result of comparison indicates that the first original length and the second original length are not equal, one of the first original length and the second original length as a jam determining value;
• and
• a control unit that performs jam determination control based on the jam determining value.