SUBSTRATE PROCESSING APPARATUS

PROBLEM TO BE SOLVED: To provide a substrate processing apparatus capable of independently performing density control with little effect by a process liquid because the process liquid density can be directly detected, and accurately performing substrate chemical processing.SOLUTION: A substrate processing apparatus for soaking a substrate in a process liquid composed of chemical and diluted solution for processing comprises: a processing tank 1 for storing the process liquid; heating means 2 and 3 for heating the process liquid; temperature detection means 4 for detecting a process liquid temperature; temperature control means 5 for operating the heating means 2 and 3 so that the process liquid temperature approaches to a set temperature; replenishment means 6 for replenishing the process liquid with the diluted solution; density detection means 7 for detecting a process liquid density by measuring the light absorption characteristics of the process liquid; and density control means 8 for operating the replenishment means 6 so that the process liquid density approaches to a set density.