PURPOSE: To prevent a cold/hot air from being blown out in a factory as otherwise taken place when a flow rate through a coil is restricted, by arranging an air conditioner to be applied in the factory such that an external air damper is caused to open for rendering a fan inoperative upon an air flow rate adjusting valve being throttled to a less opening than a preset opening amount at the rise of temperature inside the factory higher above a preset level.

CONSTITUTION: A temperature 12 inside a factory and the opening amount 11 of two-way valve are inputted to a CPU18 via an A/D converter 19. In response to this input, the CPU18 executes predetermined computations and controls via an interface 15 a fan 8, driving cylinders 3AW6A of respective external air, internal air and by-pass dampers and a two-way valves 10. When an atmospheric pressure inside the factory rises above a preset level and a flow rate adjusting valve is throttled to a less opening than a preset amount, the CPU18 actuates respective cylinders 3AW6A for causing an external air damper 3 to open, while simultaneously closing an internal air damper 4 and a by-pass damper 6. The CPU18 further instructs a two-way valve 10 to open at a preset amount for thereby rendering a fan 8 inoperative. In this manner, a comfortable atmosphere inside the factory is maintained.