PURPOSE: To lay an electric cable with an unmanned air-transporting device by discriminating the topography from an electric cable laying work starting point to an ending point and controlling the air-transporting device carrying a cable drum wound with the electric cable so that the device can fly along the optimum and shortest laying route.

CONSTITUTION: A picture analyzing device 4 analyzes the observation data of an observing device 1 obtained by observing electromagnetic waves reflected or radiated from an area and stores the topographic data of each small area in a topographic data storing device 5. A future topography estimating device 6 outputs near future topographic data on the basis of the past and current topographic data stored in the device 5 and an area evaluating device 7 gives a evaluation value to each small area upon receiving the near future topographic data. A laying route deciding device 8 decides the electric cable laying route of the shortest distance from an electric cable laying work starting and ending points and evaluation value data given to the small areas. A navigation controller 9 controls an air-transporting device carrying a cable drum wound with the electric cable so that the device can fly along the laying route.