To improve a heat exchanger for air conditioning to significantly increase heat exchange efficiency, to reduce the cost of manufacturing, and to obtain the uniform quality of products.

A main pipe 6 is embedded in the ground below a floor 1. A vertical partition wall 7 is integrally installed in the main pipe 6. These members are preferably formed of aluminum alloys. An air stream blown by a blower 5 in a direction of an arrow a flows in a direction of an arrow h to j and is discharged in a direction of an arrow k. During the downward flow along the arrow h and the upward flow along the arrow j, the flowing air is heat-exchanged with the ground through a pipe wall of the main pipe 6 and cooled in summer and heated in winter. Thereby, the air stream is cooled and heated in both the outward path (arrow h) and the return path (arrow j).