To provide a cooling device with a heat exchanger having improved cooling efficiency if not consistent in the quantity of cooling air.

The cooling device M comprises: the heat exchanger 9 formed in a flat shape for cooling air with the passage of the cooling air w; an air distribution chamber provided on one side of the heat exchanger 9 extending to the longitudinal direction for distributing air flowing therein; an inlet duct 15 formed extending to the air distribution chamber; an air collecting chamber 11 provided on the other side opposite one side of the heat exchanger 9 extending to the longitudinal direction for collecting the cooled air, and an outlet duct 16 formed extending to the air collecting chamber 11. The heat exchanger 9 has a high efficiency core portion E1 having high cooling efficiency in a region near a flow path center line L1 of the inlet duct 15 and a low efficiency core portion E2 having low cooling efficiency in a region far from the flow path center line L1.