PURPOSE: To improve a substrate cleaning effect by reducing the upper space of a cleaning tank to a reduced pressure state when gas is introduced from below into the tank and substrates are cleaned in a state that many bubbles are generated in cleanser.

CONSTITUTION: Many bubbles generated from a bubbler 10 are floated in cleanser in a lower chamber 4, and introduced into a cleaning tank 5 while being dispersed by pores 2a of a partition plate 2. In this case, since an upper chamber 3 is reduced to a reduced pressure state, volume of the bubbles in the cleanser is increased as compared with the state that the chamber 3 is set to the atmospheric pressure, and bubble rising speed is raised. Thus, cleaning effect generated by the rise of the bubbles while in contact with substrates W in the tank 5 is improved as compared with the case of the atmospheric pressure state. Since a collision force when the bubbles are broken at the surface of the cleaner in the tank 5 is increased as compared with the case of the atmospheric pressure, the cleaning effect generated by transfer of the impact force to the surfaces of the substrates through the cleanser is also improved.