An air-conditioning device capable of obtaining a suitable blow-out temperature through one passage from the initial period of change even when the air-conditioning operation in which either a first passage or a second passage is closed is changed into an operation condition in which it is opened. A feet mode in which the hot air is blown to the feet of a passenger from a second passage 7, is changed to a bilevel mode in which a first passage 6 that communicates with the upper half body of the passenger is switched from the closed state to the open state. During a predetermined period of time in the initial period following the change, the temperature blown from the first passage 6 is determined based upon a blow-out temperature of the second passage 7 and a desired blow-out temperature TAOV of the first passage 6. At the time of changing the mode, therefore, even when a first temperature sensor 25 is detecting a temperature near a desired blow-out temperature of the first passage 6 before the mode is changed, the air of the present temperature is not blown from the first passage 6 but, instead, a by-pass opening/closing damper 15 is opened, so that the air of a low temperature is blown from the first passage 6.