Image forming apparatus that identifies sheet thickness

An image forming apparatus comprising:

• a paper feeding section that feeds a sheet;
• a transport device that transports the sheet;
• a transmitter that transmits an ultrasonic wave of a predetermined volume;
• a reflected ultrasonic wave receiver that receives a reflected ultrasonic wave, transmitted from the transmitter and reflected by the sheet;
• a permeated ultrasonic wave receiver that receives a permeated ultrasonic wave, transmitted by the transmitter and permeated through the sheet;
• a volume detector that detects a reflected volume of the reflected ultrasonic wave and outputs reflected volume information, and also detects a permeated volume of the permeated ultrasonic wave and outputs permeated volume information;
• and
• a decider that identifies a thickness of the sheet being transported by the transport device, and decides whether multifeed of sheets is occurring, on a basis of a comparison result between the reflected volume indicated by the reflected volume information and a reference reflected volume, and a comparison result between the permeated volume indicated by the permeated volume information and a reference permeated volume.