Abstract: An ultrasonic wave that is transmitted from an ultrasonic-wave transmitter 1 is received by an ultrasonic-wave receiver 2, through a sheet 4. A reception signal is input to an extracting unit 19. The extracting unit compares its phase with a phase of a reference signal output from a reference-signal reproduction unit 18. It converts a phase difference therebetween into a signal having a level corresponding to the phase difference. The signal having a level corresponding to the phase difference is compared with a threshold value set in a threshold-value setter 20, by a comparator 21. When one sheet 4 is fed, the comparator 21 produces a signal of high level. When a doubles feeding occurs, it produces a signal of low level.

Abstract: The information processing device includes a first device (31) supplied with power and a second device (32) supplied with power from the first device (31) when connected to the first device (31). The information processing device includes a detection portion (121-1, 121-n, 221-1, 221-n) detecting the attachment/detachment of the second device (32) and a supply portion (121-2, 221-2) supplying power to the second device (32), and the first device (31) includes a control portion (151) controlling the supply of the power by the supply portion (121-2, 221-2) according to the result of detection by the detection portion (121-1, 121-n, 221-1, 221-n). As the supply of the power by the supply portion (121-2, 221-2) is controlled according to the result of the detection by the detection portion (121-1, 121-n, 221-1, 221-n), the electric shock on an internal circuit of the second device (32) at the time of attachment/detachment of second device (32) can be prevented.