Image processing apparatus

A double feed monitoring system, comprising:

• a transmitter that transmits an ultrasonic wave to a conveyance path through which a sheet is conveyed;
• a receiver that faces the transmitter with the conveyance path in between, and receives the ultrasonic wave transmitted by the transmitter;
• a comparison circuit that compares a level signal indicating a reception level of the ultrasonic wave received by the receiver with a threshold signal for determining whether or not sheets are double-fed in the conveyance path, and outputs a comparison result signal according to a comparison result;
• a control component configured to determine whether or not there is a possibility of a defect in a double feed detection function of detecting double feed based on the comparison result signal and the level signal;
• an amplifier circuit that amplifies a signal output by the receiver and outputs the amplified signal as the level signal;
• a DA converter that converts a digital signal indicating the threshold signal output from the control component into an analog signal and outputs the converted signal as the threshold signal;
• and
• a drive circuit that outputs a drive signal to the transmitter according to an instruction from the control component, wherein
• when outputting the drive signal to the transmitter, the drive circuit outputs the drive signal to the control component, and
• the control component determines whether or not there is a possibility of a defect in the double feed detection function based on the drive signal in addition to the comparison result signal and the level signal.