PURPOSE: To obtain an inner diameter blade flattening control method with a reduction of a blade displacement at a position inside a work to be cut in a control method for flattening an inner peripheral blade used for cutting a rigid and brittle material, such as a semiconductor ingot.

CONSTITUTION: Air nozzles 31-34 as a Bernoulli displacement means and displacement sensors 41-44 are disposed at three or more points on a blade tip part where an inner peripheral blade 2 comes into contact with a member to be cut 6, the full blade tip inner periphery, and the full surface of a blade core part. During the cutting of a rigid and brittle material, a displacement generated in the inner peripheral blade 2 is detected by the displacement sensors 41-44 and suppressed by the air nozzles 31-34 for setting the partial or full surface of the inner peripheral blade 2 in a reference position. In this manner, a blade displacement at a position inside a work to be cut is reduced.