Abstract: When substrates are immersed in a treating solution stored in an inner tank, micro bubbles are formed in large quantities. Nitrogen gas nozzles supply nitrogen gas to the surface of the treating solution, while the substrates are immersed in the solution. The nitrogen gas supplied drives the bubbles on the surface from the inner tank to an outer tank, thereby removing the bubbles from the inner tank. Since the bubbles are driven to the outer tank while the substrates are immersed, particles have a reduced chance of adhering to the substrates when the latter are withdrawn up from the treating solution in the inner tank.