A heating-use heat exchanger which includes a first heater core which exchanges heat between a first liquid and air blown into a passenger compartment and a second heater core which exchanges heat between a second liquid which is higher in temperature and smaller in flow rate than the first liquid and blown air which is heated by the first heater core is held in an air-conditioning case so that an inlet side tank part is at the bottom and an exit side tank part is at the top and the tube longitudinal direction is slanted. Due to this, the high temperature second liquid flowing into the second heater core is stored inside of the inlet side tank part in a region above the tube inlet side ends over the entire stacking direction of the plurality of tubes, then flows into the plurality of tubes.