A sound-source separation method of forming a directivity in a specific direction relative to a pair of input signals, the method comprising: a filtering step of performing filtering containing a delay by a specific time on one of the pair of input signals; and an outputting step multiplying, after the filtering step, the pair of input signals (InL(k), InR(k)), by a sequentially updated coefficient m and outputting resultant signals (OutL(k), OutR(k)), wherein: the specific time in the filtering step is equivalent to a time difference of sound wave that reaches a pair of microphones (L,R) from the specific direction; and in the filtering step, the pair of input signals originating from the sound wave from the specific direction is adjusted so as to have a same amplitude and a same phase; characterized in that the method further comprising the steps of: an interchanging step of, after the filtering step, alternately interchanging the pair of input signals (InL(k), InR(k)) through an interchanging circuit for each sampling, and generating a pair of interchanged signals (InA(k), InB(k)); a generating step of multiplying one of the interchanged signals by a coefficient m calculated one sampling before (m(k-1)), and generating an error signal between the interchanged signals by calculating a difference between the one of the interchanged signal (InA(k)) multiplied by a coefficient m calculated one sampling before (m(k-1)) and the other of interchanged signal (InB(k)); an updating step of calculating with the following recurrence formula of the coefficient m containing the error signal, and updating the coefficient m for each sampling m k = m k − 1 * β + − m k − 1 * InA k + InB k * μ * InA k; wherein β is a constant and μ is a step-size parameter that is smaller than 1. a filtering step of performing filtering containing a delay by a specific time on one of the pair of input signals; and an outputting step multiplying, after the filtering step, the pair of input signals (InL(k), InR(k)), by a sequentially updated coefficient m and outputting resultant signals (OutL(k), OutR(k)), wherein: the specific time in the filtering step is equivalent to a time difference of sound wave that reaches a pair of microphones (L,R) from the specific direction; and in the filtering step, the pair of input signals originating from the sound wave from the specific direction is adjusted so as to have a same amplitude and a same phase; characterized in that the method further comprising the steps of: an interchanging step of, after the filtering step, alternately interchanging the pair of input signals (InL(k), InR(k)) through an interchanging circuit for each sampling, and generating a pair of interchanged signals (InA(k), InB(k)); a generating step of multiplying one of the interchanged signals by a coefficient m calculated one sampling before (m(k-1)), and generating an error signal between the interchanged signals by calculating a difference between the one of the interchanged signal (InA(k)) multiplied by a coefficient m calculated one sampling before (m(k-1)) and the other of interchanged signal (InB(k)); an updating step of calculating with the following recurrence formula of the coefficient m containing the error signal, and updating the coefficient m for each sampling m k = m k − 1 * β + − m k − 1 * InA k + InB k * μ * InA k; wherein β is a constant and μ is a step-size parameter that is smaller than 1. the specific time in the filtering step is equivalent to a time difference of sound wave that reaches a pair of microphones (L,R) from the specific direction; and in the filtering step, the pair of input signals originating from the sound wave from the specific direction is adjusted so as to have a same amplitude and a same phase; characterized in that the method further comprising the steps of: an interchanging step of, after the filtering step, alternately interchanging the pair of input signals (InL(k), InR(k)) through an interchanging circuit for each sampling, and generating a pair of interchanged signals (InA(k), InB(k)); a generating step of multiplying one of the interchanged signals by a coefficient m calculated one sampling before (m(k-1)), and generating an error signal between the interchanged signals by calculating a difference between the one of the interchanged signal (InA(k)) multiplied by a coefficient m calculated one sampling before (m(k-1)) and the other of interchanged signal (InB(k)); an updating step of calculating with the following recurrence formula of the coefficient m containing the error signal, and updating the coefficient m for each sampling m k = m k − 1 * β + − m k − 1 * InA k + InB k * μ * InA k; wherein β is a constant and μ is a step-size parameter that is smaller than 1. an interchanging step of, after the filtering step, alternately interchanging the pair of input signals (InL(k), InR(k)) through an interchanging circuit for each sampling, and generating a pair of interchanged signals (InA(k), InB(k)); a generating step of multiplying one of the interchanged signals by a coefficient m calculated one sampling before (m(k-1)), and generating an error signal between the interchanged signals by calculating a difference between the one of the interchanged signal (InA(k)) multiplied by a coefficient m calculated one sampling before (m(k-1)) and the other of interchanged signal (InB(k)); an updating step of calculating with the following recurrence formula of the coefficient m containing the error signal, and updating the coefficient m for each sampling m k = m k − 1 * β + − m k − 1 * InA k + InB k * μ * InA k; wherein β is a constant and μ is a step-size parameter that is smaller than 1.