To provide a heat exchanger of high efficiency, a heat exchanging system and the like capable of being easily processed without causing the irregularity of pitches of a pipe of the heat exchanger, and further facilitated in construction at burying.

The pipe 5 is wound along a spiral groove 3 of the outer face of a spirally-grooved pipe 7, and when the pipe 5 is wound to one end of the spirally grooved pipe, it passes the inside of the spirally grooved pipe 7 to be penetrated through in a direction to the other end. When fluid is allowed to flow in the pipe 5, it flows in the pipe 5 spirally wound along the spiral groove 3 around the spirally grooved pipe 7, and further flows in the pipe 5 penetrated through the inside of the spirally grooved pipe 7 when it flows to the end of the spirally grooved pipe 7. Heat is exchanged between the fluid and surrounding geothermal heat and the like during a time when the fluid flows in the heat exchanger 1.