Provided is a vehicle air conditioner which includes a simple water-proofing structure that is capable of preventing flooding of a vehicle cabin from mating surfaces, etc. of expansion-valve covers and top and bottom divided cases of an air conditioning unit (HVAC unit) without employing a water-proofing cover, or the like. In a vehicle air conditioner in which expansion-valve covers (6 and 7) that are horizontally divided into two parts are provided at an outer surface side of top and bottom divided cases of an air conditioning unit disposed in the vehicle cabin so as to bridge mating surfaces of the cases; an expansion valve can be disposed inside the expansion-valve covers (6 and 7); and, in addition, the interior of the expansion-valve covers (6 and 7) communicates with an engine compartment via an opening provided in a toe board, step portions (11) in which inner surface sides (9) are made lower and outer surface sides (10) are made higher are formed at the top and bottom mating surfaces of the expansion-valve covers (6 and 7).