1. An information processing device comprising: chord progressions extraction means for extracting chord progressions by analyzing waveforms of musical compositions; first featuring quantity extraction means for extracting a first probability indicating the probability of given chords appearing simultaneously in each of said chord progressions; second featuring quantity extraction means for extracting a second probability indicating the probability of transition from a given chord to another chord in a chord progression in question; and calculation means for calculating first similarities between a chord progression and another chord progression, on the basis of the first probability and the second probability for each chord comprising the extracted chord progressions.