Provided is a heat exchanger. The heat exchanger includes a plurality of refrigerant tubes in which a refrigerant flows, a heat dissipation-fin in which the plurality of refrigerant tubes are inserted and through which the refrigerant and a fluid are heat-exchanged with each other, a header coupled to at least one side of the plurality of refrigerant tubes to define a refrigerant flow space, and a guide device disposed within the header to branch the refrigerant into a plurality of passages corresponding to the plurality of refrigerant tubes.