PURPOSE: To detect wrong sorting, jamming or the like in an automatic sorter for sorting articles such as letters, by using a position detection signal from a position detector mounted upstream to a branched portion, and a direction converter control signal from a conveyance section controller.

CONSTITUTION: A position detections signal 101 is generated by a position detector 21, which detects the position of a conveyed article and is mounted upstream to a branched portion (i) for performing automatic sorting from a conveyance passage 10. The signal 101 is delayed by a prescribed time by a circuit 50 to generate a position detection delay signal 103. A direction converter control signal 102 is generated by a conveyance section controller 40 and delayed by a prescribed time by a circuit 60 to generate a direction converter control delay signal 104. When abnormal conveyance is detected by using the delay signals 103, 104 and a position detection signal 105 from a position detector 22 mounted upstream to a branched portion (i+1), an abnormal conveyance detection signal 106 is sent out from a circuit 70.