To reduce a strain applied onto an optical fiber.

External force such as a stress and the strain applied onto the optical fibers 35, 36 is reduced since the fibers 35, 36 are inserted into copper pipes 39, 40. A bending strain of a trolley line main body 31 in wire drawing and a bending strain of the main body 31 in drum winding are reduced because an excessive length is given for the inserted optical fibers when cross-sectional shapes of the copper pipe 39, 40 are elliptical. The optical fibers 35, 36 are prevented from being moved by vibration of a pantograph when jelly-like inclusions 37, 38 are inserted inside the copper pipes 39, 40.