PURPOSE: To inspect the corrosion, disconnection, etc.. in the internal layer of an aerial cable by relatively rotating plural clamps gripping the cable with a twisting mechanism, by disentangling the twist of the cable to expose the internal layer and by taking photographs of the exposed parts.

CONSTITUTION: When a travel command is issued by radio control, a traveller 2 travels on an aerial cable 1 up to the position to be inspected. It stops when the position to be inspected is ascertained. After the aerial cable 1 is equipped with both clamps 4A and 4B close to the positions, front and rear, of the traveller 2, it is equipped with a clamp 3 in the foremost position, to which by a twisting mechanism 5 by giving twisting force in the direction where the strands in the external layer of the aerial cable 1 are loosened, the twist of the aerial cable 1 is disentangled and its internal layer is exposed. Then, the pictures in the internal layer taken by a camera 6 are sent by radio to a control room on the ground. In the control room necessary steps are taken either by putting it on the video how matters stand in the internal layer or by visually observing the internal layer by operators.