Heat exchanger

A heat exchanger including two or more cores welded together and each including two or more types of passage layers which are layered alternately and through which two or more fluids at different temperatures flow, the heat exchanger comprising:

• a lower header tank which entirely covers bottom portions of the cores and makes the fluids flow into the cores;
• a dummy layer which is provided at least beside a weld side face of each core, and through which none of the fluids flow;
• a weld spacer which is fixed to a peripheral edge of a side plate of the dummy layer;
• a through-hole which is made near a lower end of the side plate of the dummy layer, and through which liquid in the dummy layer is drained into a space defined by the weld spacer;
• and
• a liquid drain hole which is made at a lower corner of the weld spacer, and through which the liquid in the space is drained.