An audio signal processing apparatus includes: an obtaining unit which obtains a stereo signal including an R signal and an L signal; a control unit which generates a processed R signal and a processed L signal by performing (i) a first process of convolving pairs of right- and left-ear head related transfer functions into the R signal so that a sound image of the R signal is localized at each of two or more different positions at a right side of a listener; and (ii) a second process of convolving pairs of right- and left-ear head related transfer functions into the L signal so that a sound image of the L signal is localized at each of two or more different positions at a left side of the listener; and an output unit which outputs the processed R signal and the processed L signal.