A heat exchanger includes a core portion including a plurality of tubes, and header tanks located on opposite ends in the longitudinal direction of the plurality of tubes and communicate with the plurality of tubes. A first fluid flows through a first tank chamber and a first tube group of the plurality of tubes. A second fluid different in temperature range from the first fluid flows through a second tank chamber and a second tube group of the plurality of tubes connected to the second tank chamber. The heat exchanger includes a flow rate limiting portion. The flow rate limiting portion is configured to reduce a flow rate of the first fluid or the second fluid supplied to at least first one tube of the plurality of tubes from a boundary portion provided by the partition wall.