PURPOSE: To secure remote controlability without being regulated by a radio law by transmitting/receiving a control signal from a ground part to a working machine and an information signal from the working machine to the ground part by radio through a leakage coaxial cable.

CONSTITUTION: The working command signal of an operation means 10 in the ground part 4 is transmitted from a fixed transmitter 11 to a leakage coaxial cable 20 to be made radio and received by a traveling receiver 33 in the working machine 3 traveling along a guide provided for a steel construction to working-control a traveling motor 31 and a mounting device 32. Besides, the information signal from the mounting device 32 in the working machine 3 is made radio by traveling transmitter 34 and transmitted to the ground part 4 by way of the leakage coaxial cable 20 to be received by a fixed receiver 12. By using the leakage coaxial cable 20 like this, a feeble radio signal can be transmitted in a long distance and the non-contact state of the working machine 3 and the leakage coaxial cable 20 is secured.