PURPOSE: To provide a method and a device for detecting a leakage in the fusion part of the terminal contact plug of a cross guidepath wire in which air-tightness in the fusion part of the terminal contact plug of a cross guidepath wire can be confirmed.

CONSTITUTION: In a fusion part 5 in which the end part of a flat type cross guidepath wire 1 and a terminal contact plug 2 are melted and fixed by using a fused resin material, as the whole width of the flat type cross guidepath wire 1 in the vicinity of the terminal contact plug 2 is pressed down in the direction of the thickness, compressed air is supplied into the terminal contact plug 2 through a pipe for extracting the lead wire of the terminal contact plug 2, and at that time the air-tightness of the fusion part 5 can be detected with the existence of the leakage of air out of the fusion part 5.