Heating-medium heating unit and vehicle air conditioner using the same

A heating-medium heating unit (10), comprising a flat PTC heater (40), a first heating-medium circulation box (A) in which a plurality of box components (20,21,30) are stacked one on another, which is in close contact with one surface of the PTC heater (40), and in which a heating-medium circulation passage (33) is formed in the interior, and a second heating-medium circulation box (B) in which a plurality of box components (50,51) are similarly stacked on one another, which is in close contact with the other surface of the PTC heater (40), in which a heating-medium circulation passage (54) is formed in the interior, and which is joined to the first heating-medium circulation box (A) in a liquid-tight manner. A heating medium that circulates through the heating-medium circulation passages (33,54) in the first and second heating-medium circulation boxes (A,B) is heated, in operation, by heat radiated from both surfaces of the PTC heater (40), and PTC modules (41a,41b,41c) that constitute the PTC heater (40) are disposed in a plurality of rows along the channel direction of the heating-medium circulation passages (33,54), the plurality of PTC modules (41a,41b,41c) have different widths, and ON/OFF states of the PTC modules (41a,41b,41c) can be individually controlled.