The signal value x(t) of the transmission acoustic signal, the signal value y(t) of the observation acoustic signal, and the value g(t) of the impulse response have the relationship defined by the following expression (1).
[Math. 1]
y(t)=∫₀^tx(t)g(t?τ)dτ??(1)

Values X(f), Y(f), and G(f) respectively obtained by Fourier transforming x(t), y(t), and g(t) have the relationship defined by the following expression (2). Here, f is a frequency band, and G(f) is a transfer function.
Y(f)=G(f)X(f)??(2)

Subsequently, the feature extraction means 104 calculates a feature value from the acoustic property calculated by the acoustic property calculation means 103 (step S104). As the feature value, the impulse response or the transfer function calculated as the acoustic property may be used directly. In detail, the feature extraction means 104 may use, as the feature value, the value of the impulse response at each time or the value of the transfer function at each frequency as the acoustic property. Alternatively, the feature extraction means 104 may calculate a feature value obtained by performing principal component analysis and dimensional compression on the impulse response or the transfer function as the acoustic property, or a mel-frequency cepstrum coefficient (mfcc) described in Non Patent Literature (NPL) 1.