PURPOSE: To provide a transmission-line monitoring apparatus, which can acquire the state of a transmission line by recording a picture when the abnormal shake of the transmission line is detected in the apparatus, wherein a color camera is provided on a steel tower and the abnormal shake of the transmission line is automatically detected based on the picture of the color camera.

CONSTITUTION: A color camera 1 having a color extracting means 2 for extracting only the color of a transmission line is provided on a steel tower. The position of the center of gravity of the transmission line is measured by using the picture obtained by the color extracting means 2. The difference between the position of the center of gravity and the reference position of the center of gravity of the transmission line is computed. When the difference becomes larger than a certain threshold value, it is judged by a judging means 7 that the transmission line is abnormally shaking. A picture recording means 9 displays the warning based on the signal outputted from the judging means 7 and records the picture of the color image at the time of the abnormality in a VTR and the like.