PURPOSE: To facilitate a flow of coolant liquid and remove defects due to cutting by masking use of warpages of a wafer caused by the crystal anisotropy of signal-crystal gallium arsenide and by cutting the monocrystal while giving relative movement for keeping the cut-in side of an inner peripheral blade cutter to be opened at all time.

CONSTITUTION: At the time of cutting start, a single-crystal gallium arsenide (GaAs) ingot 2 is set so that a carbon base 5 comes to the side surface and, at the same time of cutting start, the ingot 2 made to move upward and then to rotate oppositely to the rotating direction of an inner peripheral blade cutter 1 about the central point O. By masking use of the nature in which the surface of GaAs warps to the opposite of the ingot 2, the ingot 2 is so rotationally controlled that GaAs comes to the inlet side of the inner peripherasl cutter 1, and thus cutting is effected in order that coolant liquid reaches the cutting part at all time. Thus, finally, cutting is conducted at the position where the carbon base 5 comes below the ingot 2, thereby cutting off the wafer 3.