To provide a method of cutting a silicon semiconductor wafer, which avoids the problem of a normal rotary cutting and can enjoy the merit of prolongation of the life of an inner peripheral blade.

While a holding board vacuum-holding a wafer W repeats a forward and reverse rotation less than one rotation to a rotating inner peripheral blade 1, it makes cutting of the wafer progress by the rectilinear motion and before the blade 1 ends the cutting of the wafer, the rotation of the holding board is stopped to make the cutting of the wafer continue by the rectilinear motion only and when the blade 1 cuts in a reinforced part P, the wafer on the side, which is cut down, of the wafer is held by another standing-by suction holding board and thereafter, the part P is cut and is separated from the wafer.