PURPOSE: To facilitate measurement, by attaching a camera, whose focal distance is determined, on a running vehicle, which runs on an overhead power transmission line, taking a picture of a body in the close proximity, and measuring the distance between them based on the film.

CONSTITUTION: A driving roller 1 of a running vehicle A is rotated by a motor 2 through a belt 3 and moved along a power transmission line C. A disk cam 6 with a protruded part 6a is attached on the same axis of a running roller 5 of the vehicle A. The tip part of a release 7 is fixed to a seat 9 directly beneath the cam 6. A camera 10 having a built-in automatic winding mechanism is attached under the vehicle A. A shutter button 8 can be depressed by the protruded part 6a. The button 8 is depressed automatically at every one turn of the cam 6 and the body in the close proximity of the wire C can be continuously photographed. Therefore the area, which can not be measured so far, can be simply measured.