The effect of water discharge through a slit on cavitation suppression of a blade is studied experimentally. The slit is made vertically or obliquely to the suction surface and the position is at a distance of about a 10% chord from the leading edge. With increasing discharge rate, the length of the cavity on the suction surface becomes shorter and the vibration of blade and the noise become smaller. The observations by a high-speed video camera and by the pressure gauge buried in the blade surface show that the scale of unsteady behavior of cloud cavitation becomes small due to the water discharge. Moreover, the pressure on the suction surface becomes large due to the water discharge. It seems that this pressure increase contributes to the suppression of cavitation.