The object of this invention is to improve the distribution of coolant flowing at a very low flow rate and achieve uniformity in the output air temperature while ensuring that the structure does not create excessive resistance against the coolant flow at a high flow rate. A heat exchanger 1 includes at least a plurality of tubes 2 and an upper tank 4 communicating with an upper end portion of a tube group formed by the tubes 2 so as to distribute coolant along the up/down direction. The coolant flows in through an inflow port 9 located at the upper tank 4 in the heat exchanger 1. An open-top coolant intake guide passage 25 is disposed at the inflow port 9 and the coolant intake guide passage 25 is thus inserted at the upper tank 4.
