A dicing blade (2) which rotates at high speed is surrounded by a case (3). A semiconductor wafer (1) is cut by a dicing device in which the case is filled with a cooling water (4). The case (3) is provided with a cooling water nozzle (8) for continuously supplying the cooling water and a gap (10) for discharging the cooling water out of the case. By adjusting a supply rate and a discharge rate of the cooling water, a proper water pressure can be applied to an inside of the case, thereby making it possible to cool the dicing blade and the cutting point with efficiency. As a result, it is possible to suppress chipping and cracking of the semiconductor device due to lack of cooling.