This paper proposes a sound source separation method using image signal processing and a microphone array. First, a spatio-temporal sound pressure distribution (STSPD) image is formed based on microphone outputs. Two-dimensional fast Fourier transform (2D FFT) transforms this image into a spectrum, in which sounds from different directions are separated into the components on different lines naturally. To separate sound sources, every line in the spectrum is extracted and 2D inverse FFT is applied. A method to restore a fine STSPD image from the sparse-microphone array is also proposed. Although the basic performance of the proposed method is comparable to a conventional delay and sum array, methods that are more sophisticated can be applied for improved performance.