The low-frequency internal friction in the magnetization process, where magnetic field increases linearly, is measured for (Bi0.8Pb0.2SrCaCuOy) in superconducting state by using a frequency variable inverted torsion pendulum system. Experimental conditions are as follows: measure temperature: 95 K, at which specimen is in resistance- free state; frequency: 0.5 Hz to 5 Hz. The characteristics of internal friction (IF) peak observed in curve of IF vs magnetic field strength H are as follows. 1. The peak height increases with an increasing of H (variance rate of magnetic field) but decreases as frequency increasing. 2. Magnetic field strength at which IF peak appears is 4-6 mT. 3. When H falis down to zero from a given value suddenly, IF peak disappears. 4. IF peak mentioned above disappears also when specimen turns to normal state.It is considered that, the eigen-IF of superconductor mentioned above during magnetization process stems from motion of quantum flux.