Method for producing chemical by continuous fermentation

A method of producing a chemical by continuous fermentation, comprising:

• a fermentation step that converts a fermentation feedstock, through fermentation by culturing a microorganism or culture cells, into a fermented liquid containing the chemical by a fermentation tank;
• and
• a membrane separation step that collects the chemical, as a filtrate, from the fermented liquid with the use of a plurality of separation membrane modules, and returning a non-filtered liquid to a fermented tank,
• wherein, in the membrane separation step, an intermittent filtration treatment is performed such that a filtration treatment and a filtration-stop treatment are alternately repeated with the plurality of the separation membrane modules, and
• timing of the filtration-stop treatment in each separation membrane module is controlled during the intermittent filtration treatment.