To provide a chemical supply system in which chemical can be supplied stably to a processing unit and various problems in the production process of semiconductor device can be overcome.

A chemical supply system 1 for supplying a processing unit 12 with chemical produced by mixing an original liquid with a dilution liquid is provided with a plurality of means 2 for storing the chemical, main piping 3 connecting between each of the plurality of chemical storing means 2 and the processing unit 12, means 5 for supplying the chemical from each of the plurality of chemical storing means 2 to the processing unit 12 through the main piping 3, a first circulation piping 6 for returning the chemical extracted from each of the plurality of chemical storing means 2 back to the chemical storing means 2 from which the chemical is extracted, and second circulation piping 4 for returning the chemical transported to just in front of the processing unit 12 by the chemical supply means 5 through the main piping 3 back to the chemical storing means 2 from which the chemical is extracted.