A loudspeaker and a microphone are arranged in a normal room, the loudspeaker being supplied with an impulse signal. A direct response sound from the loudspeaker and reflected sounds from wall surfaces in three directions of the normal room are converted into a response signal by the microphone. The response signal is A/D-converted, and then Fourier-transformed. The Fourier-transformed response signal is converted into a response signal with an absolute value, and then into a logarithmic response signal. The logarithmic response signal is filtered to eliminate signal components corresponding to the reflected sound. The filtered logarithmic response signal is A/D-converted, and supplied to a recorder.