A leakage current limiting device for a power transmission line, comprising: a non-conductor having a rectangular parallelepiped shape; a first input terminal installed on a first surface of the non-conductor having a rectangular parallelepiped shape and connected to a phase line (R, S, or T) of a power transmission line on an input side; a second input terminal installed on a second surface of the non-conductor having a rectangular parallelepiped shape and connected to a neutral line of the power transmission line on the input side; a third input terminal installed on a third surface of the non-conductor having a rectangular parallelepiped shape and connected to a ground line of the power transmission line on the input side; a first output terminal installed on the first surface of the non-conductor having a rectangular parallelepiped shape and connected to a phase line (R, S, or T) of a power transmission line on an output side; a second output terminal installed on the second surface of the non-conductor having a rectangular parallelepiped shape and connected to a neutral line of the power transmission line on the output side; a third output terminal installed on the third surface of the non-conductor having a rectangular parallelepiped shape and connected to a ground line of the power transmission line on the output side; a first conductor installed on the first surface of the non-conductor having a rectangular parallelepiped shape and connected between the first input terminal and the first output terminal; a second conductor which is installed on the second surface of the non-conductor having a rectangular parallelepiped shape and connected between the second input terminal and the second output terminal, and has a length equal to that of the first conductor and a sectional area of at least four times a sectional area of the first conductor; and a third conductor which is installed on the third surface of the non-conductor having a rectangular parallelepiped shape and connected between the third input terminal and the third output terminal, and has a length equal to that of the first conductor and a sectional area of at least four times a sectional area of the first conductor. a non-conductor having a rectangular parallelepiped shape; a first input terminal installed on a first surface of the non-conductor having a rectangular parallelepiped shape and connected to a phase line (R, S, or T) of a power transmission line on an input side; a second input terminal installed on a second surface of the non-conductor having a rectangular parallelepiped shape and connected to a neutral line of the power transmission line on the input side; a third input terminal installed on a third surface of the non-conductor having a rectangular parallelepiped shape and connected to a ground line of the power transmission line on the input side; a first output terminal installed on the first surface of the non-conductor having a rectangular parallelepiped shape and connected to a phase line (R, S, or T) of a power transmission line on an output side; a second output terminal installed on the second surface of the non-conductor having a rectangular parallelepiped shape and connected to a neutral line of the power transmission line on the output side; a third output terminal installed on the third surface of the non-conductor having a rectangular parallelepiped shape and connected to a ground line of the power transmission line on the output side; a first conductor installed on the first surface of the non-conductor having a rectangular parallelepiped shape and connected between the first input terminal and the first output terminal; a second conductor which is installed on the second surface of the non-conductor having a rectangular parallelepiped shape and connected between the second input terminal and the second output terminal, and has a length equal to that of the first conductor and a sectional area of at least four times a sectional area of the first conductor; and a third conductor which is installed on the third surface of the non-conductor having a rectangular parallelepiped shape and connected between the third input terminal and the third output terminal, and has a length equal to that of the first conductor and a sectional area of at least four times a sectional area of the first conductor.