A signal to noise power ratio estimation system for multi-carrier communication includes a phase rotator, a power estimator, a channel gain calculator, an average and selection device, a combination and calculation device and a decibel transformation device. A target output standby section holds the target output by the target output control section on standby based on an achievement status for the target. Such clamp can hold long bodies with various diameters, and also can attenuate vibrations of the long bodies.