An opening/closing control device for a grille shutter is capable of appropriately opening and closing the grille shutter according to a vehicle outside environment and an operating state of an aircon while ensuring the operation of the aircon, and is capable of sufficiently improving vehicle operating efficiency. An aircon operating time ratio as a ratio of operation time of an aircon to overall time is calculated. When the calculated aircon operating time ratio is larger than the sum of a threshold value calculated according to an ambient air temperature and a hysteresis constant, the grille shutter is opened to promote cooling of refrigerant in the aircon and reduce motive power consumed by the aircon. Therefore, it is possible to appropriately open and close the grille shutter depending on the ambient air temperature and the operating ration of the aircon.