The present invention allows biomass and/or biomass-produced components to be obtained at high yields by executing numeric simulation of flow to reasonably identify the running conditions suitable for a fermenter. The control device according to the present invention comprises an input means for entering measured data from a measurement means, which measures nutrient components, the concentrations of oxygen, carbon dioxide, and biomass in a culture medium; a computation means for calculating nutrient components uptake rate, oxygen uptake rate and carbon dioxide exhaust rate per unit amount of biomass from the measured data entered at the aforementioned input means, as well as volumetric mass transfer coefficient kLa from turbulent energy k and a turbulent energy dissipation rate e, both of which are calculated by a transport equation, as well as a diffusion coefficient D, followed by calculating the concentrations of the nutrient components, dissolved oxygen, and dissolved carbon dioxide in any area in the fermenter using an algorithm to numerically integrate a differential equation describing variations in medium components over time from the calculated nutrient components uptake rate, the calculated oxygen uptake rate, the calculated carbon dioxide exhaust rate, and the calculated volumetric mass transfer coefficient kLa; and a display means for displaying concentration distributions of the nutrient components, dissolved oxygen, and dissolved carbon dioxide in the fermenter based on the concentrations of the nutrient components, dissolved oxygen, and carbon dioxide in any area of the fermenter calculated at aforementioned computation means.