1. A sound processing device comprising: a time-frequency analysis unit which generates a time-frequency plane from a sound signal through time-frequency analysis; a region characteristic amount extraction unit which, for a plurality of partial region pairs which is defined on the time-frequency plane and of which at least either of shapes of two partial regions or positions of the two partial regions differ from one another, extracts a region characteristic amount from each partial region; and a sound identifier generation unit which generates a sound identifier which identifies the sound by using the region characteristic amount from the each partial region.