A leakage current detection device comprising: a leakage current detector that detects a leakage current flowing through an electric line to be measured in a three-phase four-wire system in which three phases (phase R, phase S, and phase T) are star-connected, a neutral point is grounded, and a grounding wire is lead out; a voltage detector that detects a voltage applied between any two of the three phases in the electric line to be measured; a phase difference detector that detects a phase difference based on the leakage current detected by the leakage current detector and the voltage detected by the voltage detector; and a resistive component leakage current calculator that calculates a resistive component leakage current which is attributed to a ground insulation resistance and contained in the leakage current flowing through the electric line to be measured based on the phase difference detected by the phase difference detector and the leakage current detected by the leakage current detector; characterized in that the device further comprises: a determination processor that determines whether or not the phase difference detected by the phase difference detector is within a predetermined range and if the phase difference is determined not to be within the predetermined range, transmits the phase difference detected by the phase difference detector to the voltage detector, wherein the voltage detector is switched so as to detect a voltage applied between the other two phases in the electric line to be measured based on the phase difference transmitted from the determination processor. a leakage current detector that detects a leakage current flowing through an electric line to be measured in a three-phase four-wire system in which three phases (phase R, phase S, and phase T) are star-connected, a neutral point is grounded, and a grounding wire is lead out; a voltage detector that detects a voltage applied between any two of the three phases in the electric line to be measured; a phase difference detector that detects a phase difference based on the leakage current detected by the leakage current detector and the voltage detected by the voltage detector; and a resistive component leakage current calculator that calculates a resistive component leakage current which is attributed to a ground insulation resistance and contained in the leakage current flowing through the electric line to be measured based on the phase difference detected by the phase difference detector and the leakage current detected by the leakage current detector; characterized in that the device further comprises: a determination processor that determines whether or not the phase difference detected by the phase difference detector is within a predetermined range and if the phase difference is determined not to be within the predetermined range, transmits the phase difference detected by the phase difference detector to the voltage detector, wherein the voltage detector is switched so as to detect a voltage applied between the other two phases in the electric line to be measured based on the phase difference transmitted from the determination processor. a determination processor that determines whether or not the phase difference detected by the phase difference detector is within a predetermined range and if the phase difference is determined not to be within the predetermined range, transmits the phase difference detected by the phase difference detector to the voltage detector, wherein the voltage detector is switched so as to detect a voltage applied between the other two phases in the electric line to be measured based on the phase difference transmitted from the determination processor.