PROBLEM TO BE SOLVED: To provide an in-vivo signal source detection method capable of accurately detecting the position of an activity region (signal source) of a tissue which is active in a living body using a small number of electrodes.SOLUTION: Three electrodes 21, 22 and 23 are disposed on a circumference on a surface of a living body 10 so as to surround a plurality of muscle fibers 40. A first voltage Vgenerated when a first external resistor is connected between each electrode and a ground potential, and a second voltage V'generated when a second external resistor is connected between each electrode and the ground potential are measured, a ratio of V/V'is calculated from the first voltage Vand the second voltage V', and the position of a signal source in the living body is detected based on three ratios of V/V'.SELECTED DRAWING: Figure 1【課題】少ない数の電極を用いて、生体内で活動する組織の活動部位（信号源）の位置を精度よく検出することができる生体内信号源検出方法を提供する。【解決手段】複数の筋繊維４０を囲むように、生体１０の表面の円周上に、３つの電極２１、２２、２３を配置し、各電極とグランド電位との間に、第１の外部抵抗を接続したときに生じる第１の電圧Ｖｉと、第２の外部抵抗を接続したときに生じる第２の電圧Ｖ’ｉとを測定し、第１の電圧Ｖｉ及び第２の電圧Ｖ’ｉから、比Ｖｉ／Ｖ’ｉを算出し、これら３つの比Ｖｉ／Ｖ’ｉに基づいて、生体内の信号源の位置を検出する。【選択図】図１
