An object is to provide a compact, lightweight, low-cost heating-medium heating unit in which a plurality of flat heat-exchange tubes and PTC heaters are stacked to reduce the thermal contact resistance, thereby enhancing the heat transfer performance, as well as a vehicle air conditioner equipped with the same. The heating-medium heating unit is provided with a plurality of flat heat-exchange tubes (17) each having an inlet header (22) and an outlet header (23) at one end or both ends of flat tube portions (20) through which a heating medium is circulated; sealing materials (26) that seal the peripheries of communicating holes (24, 25) of the inlet headers (22) and the outlet headers (23) of the stacked flat heat-exchange tubes (17); PTC heaters assembled between the flat tube portions (20) of the flat heat-exchange tubes (17); and a heat-exchange pressing member (16) that presses the alternately stacked flat heat-exchange tubes (17) and PTC heaters into close contact with each other, wherein a deformation-preventing reinforcing portion (29) is provided around each of the communicating holes (24, 25) in the inlet header (22) and the outlet header (23) of each of the flat heat-exchange tubes (17).