To provide a geothermal heat collector adopted also for standard home due to its simple and inexpensive configuration and having high heat use efficiency and an ecologically-friendly air conditioning system.

The geothermal heat collector 1 includes: a hollow sealed body container 2 embedded in the ground E; and an air flowing pipe line 34 arranged within the body container 2. One end of the air flowing pipe line 34 is connected to an air inflow pipe 16 outside the body container 2, and the other end is connected to an air outflow pipe 18 outside the body container 2. A thermal storage medium 33 including phase change substances 62 having ≥20°C and ≤28°C of phase change temperature generating phase change between a solid phase and a liquid phase is arranged within the body container 2 outside the air flowing pipe line 34. Micro-capsules 63 including the phase change substances 62 may be used for the thermal storage medium 33.