An air-conditioning duct is provided inside a car console box that has an ornamental portion. The duct has an air passage for conducting conditioned air from an air conditioner to the passenger compartment. The air passage is defined by a first wall portion formed by the ornamental portion, a second wall portion opposed to the first wall portion, a third wall portion located between the first and the second wall portions, and a fourth wall portion located between the first and the second wall portions. The fourth wall portion is opposed to the third wall portion. Each wall portion has an inner surface exposed to the interior of the air passage. A pair of boundary lines are defined on the inner surface of the first wall portion at boundaries between the first wall portion and the third and fourth wall portions. A dew condensation suppression portion is provided on the inner surface of the first wall portion between the pair of the boundary lines. A space is defined between the dew condensation suppression portion and each boundary line. When the thickness of the dew condensation suppression portion on the first wall portion is expressed by T (mm), and the sum of the widths of the spaces is expressed by D (mm), the thickness T and the sum D of the widths satisfy the following expression (1). T.gtoreq.D+2 mm(D>0 mm) (1)