A band extending apparatus (1) is provided with: first generating device (111, 112) for generating a baseband signal (XB(n)) by up-sampling an input signal (X(n)) and then transmitting it through a low-pass filter; a second generating device (21) for generating a high-frequency signal (XH(n)), by extracting a signal component on a higher-frequency side of a signal which is obtained by squaring a band limited signal (Xb(n)) which is a signal component with a predetermined band of the baseband signal; and a third generating device (141) for generating an output signal (XE(n)) by adding the high-frequency signal to the baseband signal.