An information processing apparatus is provided which includes a signal conversion unit for converting an audio signal to a pitch signal indicating a signal intensity of each pitch, a melody probability estimation unit for estimating for each frame a probability of each pitch being a melody note, based on the audio signal, and a melody line determination unit for detecting a maximum likelihood path from among paths of pitches from a start frame to an end frame of the audio signal, and for determining the maximum likelihood path as a melody line, based on the probability of each pitch being a melody note, the probability being estimated for each frame by the melody probability estimation unit.