To provide a method and an apparatus for balancing a test piece at a low cost, wherein a part from which the material is removed has smooth surface.

In order to be balanced, a test piece is held by the chuck 4 of a main spindle 1 disposed vertically before being turned. A tool spindle 7 for driving a cutting tool 9 is disposed mirror symmetrically to the main spindle 1 while being shifted sideways. The test piece 5 and the cutting tool 9 are driven at the same r.p.m. in the same or reverse direction. The size and phase position of an unbalance mass to be removed are detected by means of a sensor 16 and an angle sensor 10. A cutting tool for detecting the phase angle through an angle sensor 22 is driven with same phase angle and carried toward the test piece thus removing the material. Signals are processed by means of a computer 20. A machine controller determines phase matching between the rotating unbalance mass and the tool and then produces carrying motion of tool with respect to the test piece.