A device (Fig. 29: 1000) for detecting a leak, the device comprising: an earth voltage measuring unit measuring earth voltage; an ADC unit sampling the measured earth voltage and converting the sampled earth voltage into a digital value; an effective value calculating unit calculating an effective value of the earth voltage converted into the digital value; a Fourier transforming unit performing Fourier transform of the measured earth voltage to calculate voltage for each harmonic component which is an integer multiple of a fundamental frequency - a power frequency of AC commercial power -, based on the effective value of the earth voltage; a content rate calculating unit calculating a voltage content rate of the fundamental frequency to the voltage obtained by adding the voltage for each harmonic component based on the voltage for each harmonic component; a harmonic distortion rate calculating unit calculating a total harmonic distortion and a harmonic distortion factor based on the voltage value for each harmonic component; a zero-crossing estimating unit estimating a zero-crossing count at which the earth voltage converted into the digital value passes through zero voltage for a predetermined time T1; and a suspicious earth leaking area determining unit determining that the earth voltage is generated by the leak of the AC commercial power based on at least any one of the effective value of the earth voltage, the voltage content rate, the total harmonic distortion, the harmonic distortion factor, the zero-crossing count, and the distortion count and determining a region where the earth voltage is measured as the suspicious earth leaking area based on the determination result. an earth voltage measuring unit measuring earth voltage; an ADC unit sampling the measured earth voltage and converting the sampled earth voltage into a digital value; an effective value calculating unit calculating an effective value of the earth voltage converted into the digital value; a Fourier transforming unit performing Fourier transform of the measured earth voltage to calculate voltage for each harmonic component which is an integer multiple of a fundamental frequency - a power frequency of AC commercial power -, based on the effective value of the earth voltage; a content rate calculating unit calculating a voltage content rate of the fundamental frequency to the voltage obtained by adding the voltage for each harmonic component based on the voltage for each harmonic component; a harmonic distortion rate calculating unit calculating a total harmonic distortion and a harmonic distortion factor based on the voltage value for each harmonic component; a zero-crossing estimating unit estimating a zero-crossing count at which the earth voltage converted into the digital value passes through zero voltage for a predetermined time T1; and a suspicious earth leaking area determining unit determining that the earth voltage is generated by the leak of the AC commercial power based on at least any one of the effective value of the earth voltage, the voltage content rate, the total harmonic distortion, the harmonic distortion factor, the zero-crossing count, and the distortion count and determining a region where the earth voltage is measured as the suspicious earth leaking area based on the determination result.