A cutting blade for cutting a workpiece includes a base and a cutting edge fixed to a peripheral portion of the base. The cutting edge is formed by bonding a mixture of abrasive grains and photocatalyst particles with a binder. In cutting the workpiece by using the cutting blade, a cutting water is supplied to the cutting blade and light is applied to the cutting blade to excite the photocatalyst particles. The cutting water supplied to the cutting blade comes into contact with the photocatalyst particles excited, so that the cutting water is given an oxidizing power due to hydroxy radicals.