PURPOSE: To suppress the displacement of a blade at a cutting position.

CONSTITUTION: A blade position detection sensor 5 and an electromagnet 6 are arranged in opposed relation to the blade surface 1b at the cutting position C of a blade 1. The cutting of a silicon single crystal rod 4 is started in such a state that an initial magnetic force is preliminarily applied to the blade 1 to allow the blade 1 to approach the electromagnet 6 and, when the blade 1 is displaced in the direction going away from the electromagnet 6, the magnetizing current supplied to the electromagnet 6 is increased corresponding to this displacement to negate the displacement of the blade 1. Contrarily, when the blade 1 is displaced in the direction approaching the electromagnet 6, the magnetizing current supplied to the electromagnet 6 is reduced corresponding to this displacement to negate the displacement of the blade 1.