There is provided a signal processing device, comprising: a frequency detecting means that detects a frequency satisfying a predetermined condition from an audio signal; an offset means that gives an offset to the detected frequency by the frequency detecting means in accordance with a frequency property at the detected frequency or around the detected frequency; a reference signal generating means that generates a reference signal by extracting a signal from the audio signal based on the detected frequency offset by the offset means; an interpolation signal generating means that generates an interpolation signal based on the generated reference signal; and a signal synthesizing means that performs high band interpolation by synthesizing the generated interpolation signal and the audio signal.