Provided is a heat exchanger. The heat exchanger includes a plurality of refrigerant tubes in which a refrigerant flows, a heatsink fin coupled to the plurality of refrigerant tubes to heat-exchange the refrigerant with a fluid, a header disposed on at least one side of the plurality of refrigerant tubes to define a flow space of the refrigerant and a guide device disposed in the header to partition the flow space, the guide device guiding the refrigerant from the header to the refrigerant tubes. The guide device includes a movable cover part.