A processing solution preparation and supply apparatus includes a dissolving preparation bath to which a material powder and ultrapure water are supplied. This dissolving preparation bath is connected to a substrate processing apparatus via a pipe, and a processing solution prepared from the material powder on-site is supplied to the processing apparatus. To reduce an increase in the microorganism concentration in the ultrapure water, this ultrapure water is circulated substantially constantly. This suppresses deterioration and concentration fluctuations of a processing solution for use in processing of a semiconductor substrate, when this processing solution is supplied to the use side. This also reduces particles and improves the economical efficiency.