PURPOSE: To move an upper belt while floating up it and to diminish the friction resistance by feeding the pressure water wherein the underside of upper belt is pressurized thereby.

CONSTITUTION: A feed apparatus of pressure water by which the pressure water pressurizing the underside of an upper belt 6a is fed to a belt conveyor housing chamber 3. Thereby since the upper belt 6a is moved in such state that it is approximately floated up by receiving the weight of fine sand and dirty water by means of the pressure water of the inside of the belt conveyor housing chamer 3, the friction resistance of the upper belt 6a is diminished. Furthermore the pressure water is made to a sealing wall by the -pressure balance of a fine sand settling chamber 2 and the belt conveyor housing chamber 2 and the leak of fine sand are diminished.