PURPOSE: To make greater the spread of sound of virtual stereo signal, by dividing monaural signal into two and adding the two with positive and negative phase each other after delaying one signal and level adjustment, and converting the result with a transfer function from the virtual sound source to listners.

CONSTITUTION: Monaural signal incoming from an input terminal 1 without normal position information is fed to amplifiers 2a, 2b and the outputs are added in positive and negative phase via a delay circuit 3, high pass filter 9 an level adjuster 4, to amplifiers 2a, 2b. To the virtual stereo signal thus obtained, the signal which is converted with the ratio Bi/Ai, where Ai is a transfer function between the virtual sound sources I, J and an ear of a listner closer to the sound source and Bi is that between those and another ear remote, is added at addition amplifiers 11a, 11b. Thus, sound is made as if it came form the virtual sound sources I, J in front of the listner. Further, the spread of sound can further be made by adding the indirect sound reflected from walls by means of an indirect sound addition circuit 13.