A structure including an ultrasonic transducer, a material database, and a material determination section. The ultrasonic transducer transmits ultrasound signals of a plurality of frequencies toward a printing paper over a frequency band covering 40 kHz to 100 kHz or more, and receives reflection signals. The material database stores information representing a reception signal on a material basis. The material determination section makes a material determination for the printing paper based on the information stored in the material database, and the signal (signal derived by amplifying a signal) received by the ultrasonic transducer.