PURPOSE: To provide a multi-stage continuous fermentation apparatus independently controlling the fermentation speed in individual fermentation tanks and capable of stably giving uniform final fermentation liquid.

CONSTITUTION: A substrate 32 in a raw material tank 31 in the 1st fermentation unit 49 is continuously supplied to the 1st fermentation tank 34 at a constant flow rate with a pump 36a and fermented. At the same time, a liquid mixture composed of microbial cells, residual substrate, products, etc., is continuously supplied to a cell separator 41 with a pump 36b and the separated cells are returned through a pipe 31 to the fermentation tank 34. The residual substrate, products, etc., are stored in the 1st fermentation storage tank 42. The deviation between a preset value and an indicated value of a sensor determining the composition of the fermentation liquid is measured by the sensor 43, a temperature converter 48 and an arithmetic unit 45 and the setting temperature of a temperature controller 46 for controlling the heating means of the fermentation tank 34 is adjusted according to the deviation. The reaction rate in the fermentation tank can be stabilized by the adjustment of the setting temperature.