PURPOSE: To enhance a treatment effect and, at the same time, to enhance a uniformity of a treatment by a method wherein a drain port is formed at a treatment tank near a part where a sediment of a treatment liquid inside the treatment tank is produced and a stream of the treatment liquid is produced so that a wafer can be always brought into contact with a new treatment liquid.

CONSTITUTION: A treatment tank 1 houses a wafer contained in a carrier 2 and is used for an immersion treatment; a treatment-liquid supply hole 4 supplies a treatment liquid to the treatment tank 1. A liquid-supply valve 5 is used to supply or stop the treatment liquid to the treatment-liquid supply hole 4; overflow grooves 6 are used to uniformly overflow the treatment liquid inside the treatment tank from an upper-edge face of the treatment tank. Drain holes 7 are used to drain the treatment liquid stagnating at the bottom of the treatment tank to the outside. Thereby, it is possible to prevent sediment near a boundary part between a tank wall of a cornered tank and the bottom and to sufficiently replace it with a new liquid.