A leak detection device for detecting a leak between a battery (1, 2) and a ground, the leak detection device comprising a microcomputer which comprises: a pulse signal outputting portion configured to output predetermined pulse signals to a positive connecting wire connected to a positive side of the battery (1, 2) and a negative connecting wire connected to a negative side of the battery (1, 2), wherein the positive connecting wire and the negative connecting wire are intermittently connected to a control ground via leak resistors (105, 106), respectively; a response waveform detecting portion configured to detect a positive response waveform for the pulse signal output to the positive connecting wire, input via a voltage-dividing resistor portion, and a negative response waveform for the pulse signal output to the negative connecting wire, input via a voltage-dividing resistor portion, wherein the voltage between the voltage-dividing resistor portions (301, 302) is set so as to be 1/2 of a Vcc voltage which is the upper limit of the input voltage range set for the microcomputer; and characterized in that the leak detection device further comprises an amplitude ratio calculating portion configured to calculate an amplitude ratio Rv based on: - an amplitude Vap which is the difference between a maximal value and a minimal value of the positive response waveform, - an amplitude Van which is the difference between a maximal value and a minimal value of the negative response waveform, - a difference V1 between the maximal value of the positive response waveform and the maximal value of the negative response waveform, and - a difference V2 between the minimal value of the positive response waveform and the minimal value of the negative response waveform by an expression below: Rv = Vap + Van / V 1 + V 2 wherein a leak detecting portion of the microcomputer is configured to detect the leak between at least one of the positive side and the negative side of the battery (1, 2) and the ground when the amplitude ratio Rv becomes less than a predetermined threshold value. a pulse signal outputting portion configured to output predetermined pulse signals to a positive connecting wire connected to a positive side of the battery (1, 2) and a negative connecting wire connected to a negative side of the battery (1, 2), wherein the positive connecting wire and the negative connecting wire are intermittently connected to a control ground via leak resistors (105, 106), respectively; a response waveform detecting portion configured to detect a positive response waveform for the pulse signal output to the positive connecting wire, input via a voltage-dividing resistor portion, and a negative response waveform for the pulse signal output to the negative connecting wire, input via a voltage-dividing resistor portion, wherein the voltage between the voltage-dividing resistor portions (301, 302) is set so as to be 1/2 of a Vcc voltage which is the upper limit of the input voltage range set for the microcomputer; and characterized in that the leak detection device further comprises an amplitude ratio calculating portion configured to calculate an amplitude ratio Rv based on: - an amplitude Vap which is the difference between a maximal value and a minimal value of the positive response waveform, - an amplitude Van which is the difference between a maximal value and a minimal value of the negative response waveform, - a difference V1 between the maximal value of the positive response waveform and the maximal value of the negative response waveform, and - a difference V2 between the minimal value of the positive response waveform and the minimal value of the negative response waveform - an amplitude Vap which is the difference between a maximal value and a minimal value of the positive response waveform, - an amplitude Van which is the difference between a maximal value and a minimal value of the negative response waveform, - a difference V1 between the maximal value of the positive response waveform and the maximal value of the negative response waveform, and - a difference V2 between the minimal value of the positive response waveform and the minimal value of the negative response waveform by an expression below: Rv = Vap + Van / V 1 + V 2 wherein a leak detecting portion of the microcomputer is configured to detect the leak between at least one of the positive side and the negative side of the battery (1, 2) and the ground when the amplitude ratio Rv becomes less than a predetermined threshold value.