PURPOSE: To stabilize the supply of liquid treatment agent by a method wherein a circumferential trench formed in the circumferential wall of a cup, a plurality of nozzles whose one side ends are connected to a liquid treatment agent supply source and whose other ends are linked with the circumferential trench with a predetermined interval and a partition provided vertically along the inner circumferential wall of the cup are provided.

CONSTITUTION: A number of small diameter nozzles 21a, 21a... are drilled from the inner circumference side of the annular circumferential trench 20 of a developer supply mechanism 19 provided in an upper cup 17 to compose a nozzle group 21. A cylindrical partition 22 is formed inside the nozzle group 21 with a predetermined interval so as to form a solution sink 23 and the height of the top surface of the partition 22 is at least equal to the height of the top surface 20a of the circumferential trench 20. Therefore, even if the supply of liquid treatment agent into the circumferential trench 20 is discontinued, the treatment agent remains in the solution sink formed between the partition 22 and the nozzles 21a, 21a..., so that the mingling of bubbles into the circumferential trench 20 can be avoided. With this constitution, even after the long time suspension of the apparatus, the liquid treatment agent can be supplied stably.