Vegetable factory is an industrial vegetable production system which can supply steady amount of vegetables independent of natural environmental conditions. The system, in which environmental conditions for growing vegetables are completely controlled using artificial lights, is called “completely controlled vegetable factory”. Compared with that, solar- type system is expected to have the advantage of economy and of saving energy by adding solar irradiation. In case of solar-type vegetable factory, however, there is a difficulty that varying solar irradiation effects much on the inside environmental conditions (illuminance, air temperature, and so on). So, environmental cotrol method plays a very important part to suffice both demands of yearlong steady production and of improvement of economy.<br>In order to perform economically optimum environmental control in solar-type vegetable factory, optimum criteria for inside environmental control are proposed as below.<br>1) P≥P₀<br>2) E→MAX.<br>where P: production<br>P₀: constant value of production (lower limit)<br>E index of economy<br>Production P is a function of inside environmental conditions and index E depends on both inside and outside environmental conditions. 1) is the criterion to ensure certain amount of product. 2) is the criterion for economy, and possible indices of E are, for example, the inverse of productive cost (C), cost performance (P/C), and profit (described as a form of aP-bC, where a and b are constants).<br>To make sure of the efficiency of the optimum environmental control method based on the above criteria, several cases of simulated controls are executed. The main results are as follows.<br>1) The economic efficiency of the proposed control methods are clarified, i. e. the comparison with no control and with constant-temperture control shows that our control methods work quite adaptively on outside environmental conditions and sufficiently achieve both demands of steady production and of improvement of economy.<br>2) In control on cloudy days, economy weighs more than production, differed from that on clear days. And in winter, production cost is lower on the average than in summer.<br>3) The value of P_o effects much on the control of inside environmental conditions.<br>And in case that profit is used as E, the estimate of the profit has also much influence on the inside conditions.