A double pipe type heat exchanger includes an inner pipe having a first flow path defined therein and an outer pipe arranged around the inner pipe to define a second flow path between the inner pipe and the outer pipe. The inner pipe includes a spiral groove formed on an outer circumferential surface of the inner pipe to extend along a longitudinal direction of the inner pipe. The outer pipe includes a reduced diameter portion protruding inwardly so that the inner surface of the outer pipe is intermittently contacted with the outer circumferential surface of the inner pipe.