PURPOSE: To make the measurement accurate and quick, by supporting a cable by a rotary body that is supported by a casing to which weights are attached, and measuring the degree of the twisting of the cable with respect to the casing by a rotation gage which is connected to the rotary body.

CONSTITUTION: When a cable 3 is suspended by steel towers 2 and 2, a twisting roller 17 is firmly fixed to a specified position of the cable 3. When the cable 3 is suspended and twisted around, rollers 10 which support the twisting roller 17 are rotated, since the rotation of a casing 4 is regulated by weights 7 and 7. Therefore, rotation gages 16 and 16, which are coupled with the rollers 10 and 10, measure the direction and number of rotation of the cable 3. The measured values are transmitted to a worker's receiver from an FM transmitter. The cable 3 is corrected to the adequate state based on the number and direction of twisting, and thereafter the cable is suspended between the steel towers 2 and 2. Thus the measurement can be performed accurately and quickly.