A frequency domain converter is configured to create a plurality of pieces of frequency domain information by individually converting a plurality of input audio signals, which is acquired at different positions, into frequency domain information. A relative value calculator is configured to calculate a relative value of time frequency components of at least one set of frequency domain information among the plurality of pieces of frequency domain information. A signal determiner is configured to determine whether or not each of the input audio signals includes an audio signal component, which is emitted from a predetermined position, based on whether or not the relative value is included in a range specified and based on a relative threshold value stored in a memory in advance.