An electric leakage detection method of detecting an electric leakage occurring position in a power source unit including multiple power sources (10A to 10N) electrically connected to each other, the electric leakage detection method comprising: electric leakage voltage measurement of measuring a voltage generated from the electric leakage occurring position and calculating an electric leakage voltage V L which is an electrical potential difference between a reference terminal connected to a predetermined position of the power source unit and the electric leakage occurring position based on the measured voltage; and electric leakage occurring position determination of determining the electric leakage occurring position based on the electric leakage voltage V L, the method characterized by further comprising: reference electrical potential difference obtaining of obtaining a reference electrical potential difference Vs which is an electrical potential difference between a first terminal connected to a predetermined position of the power source unit and a second terminal connected to a position with a different electrical potential from the first terminal, wherein in the electric leakage voltage measurement, either one of the first terminal or the second terminal is selected as the reference terminal, and an electric leakage voltage V L which is an electrical potential difference between the reference terminal and the electric leakage occurring position is calculated, and in the electric leakage occurring position determination, the electric leakage occurring position is determined based on a ratio (V L /V S) of the electric leakage voltage V L to the reference electrical potential difference Vs. electric leakage voltage measurement of measuring a voltage generated from the electric leakage occurring position and calculating an electric leakage voltage V L which is an electrical potential difference between a reference terminal connected to a predetermined position of the power source unit and the electric leakage occurring position based on the measured voltage; and electric leakage occurring position determination of determining the electric leakage occurring position based on the electric leakage voltage V L, the method characterized by further comprising: reference electrical potential difference obtaining of obtaining a reference electrical potential difference Vs which is an electrical potential difference between a first terminal connected to a predetermined position of the power source unit and a second terminal connected to a position with a different electrical potential from the first terminal, wherein in the electric leakage voltage measurement, either one of the first terminal or the second terminal is selected as the reference terminal, and an electric leakage voltage V L which is an electrical potential difference between the reference terminal and the electric leakage occurring position is calculated, and in the electric leakage occurring position determination, the electric leakage occurring position is determined based on a ratio (V L /V S) of the electric leakage voltage V L to the reference electrical potential difference Vs. reference electrical potential difference obtaining of obtaining a reference electrical potential difference Vs which is an electrical potential difference between a first terminal connected to a predetermined position of the power source unit and a second terminal connected to a position with a different electrical potential from the first terminal, wherein in the electric leakage voltage measurement, either one of the first terminal or the second terminal is selected as the reference terminal, and an electric leakage voltage V L which is an electrical potential difference between the reference terminal and the electric leakage occurring position is calculated, and in the electric leakage occurring position determination, the electric leakage occurring position is determined based on a ratio (V L /V S) of the electric leakage voltage V L to the reference electrical potential difference Vs.