The rotating mirror light deflecting system employs a non-circular dynamic gas bearing providing dynamic pressure to radially support the shaft. The bearing is provided internally with a multiplicity of grooves or embankments whereby dynamic gas pressure is increased to enhance rigidity. The bearing radially moves as a whole with damping according to a movement of the shaft, thus permitting nondestructive movement of the shaft and absorption of the resonant energy of the shaft. The shaft and the bearing will not come in contact with each other, and oscillation energy of the shaft is absorbed or dissipated by an external viscous or hysteresis resistance of the bearing therefore resonance oscillation is attenuated on the instant it occurs. Since the resonance point is high due to bearing surface rigidity, whirling is hard to arise, however, if whirling does arise, then the bearing and the shaft move together to attenuate oscillation energy of the shaft, therefore oscillation and whirling is put down immediately.