PURPOSE: To provide a contactless rotating machine rotor balancer simple in structure and easy to assemble without increasing leakage area or generating drift to a blade during acceleration/deceleration.

CONSTITUTION: A blade side plate 2 for connecting a blade 1 integrally to a rotating center body 6 has two kinds of built-in balance weights. One balance weight generates centrifugal force in the opposite direction to the centrifugal force of the center-of-gravity of the blade 1 and is built in on the close side (A-A' cross section) to the blade 1, and the other balance weight generates centrifugal force in the same direction as the centrifugal force of the center-of- gravity of the blade 1 and is built in on the far side (B-B' cross section) from the blade 1.