PURPOSE: To reduce the laying the space, and prevent defective contact and derailment, by a method wherein the feed rail supplying the power to mobile cranes comprises a slot of belt-shaped insulated bed plate attached to the fitting unit through a hanger and a feeding conductor extendedly mounted on the bottom face thereof.

CONSTITUTION: A trolley feed unit feeding three-phase power supply, is provided with three lines of collector guide slots 19a in parallel on the surface of the belt- shaped insulated bed plate 19 and a feeding conductor 20 is mounted extendedly on the bottom face thereof to arrange three lines of feed rail 21 comprising slots 19a and conductors 20 to be integrated with said base 19 and set to the fitting unit 22 with the hanger 23. A pair of catenary cable 24 are inserted therethrough in the longitudinal direction at both ends of said bed plate 19 and wired extendedly between the fitting units. Said collector apparatus 25 renders three collectors 27 mounted in parallel and in a body, opposingly facing said guide slots 19a, in the inner part of insulated electronic holder 26 with a "ko"(Japanese:katakana,2533)-styled section covering the surface of bed plate 19.