To provide a soil heat exchanger of a heat pump system using soil heat, constructed in a soil cement diaphragm wall constructed for retaining to a predetermined depth in a ground.

This soil heat exchanger 20 is installed in an H-shape steel 12 planted in the diaphragm wall 10 constructed according to a soil cement diaphragm wall construction method. The soil heat exchanger includes: a soil heat exchanging tube 23 provided in at least one side of groove spaces of the H-shape steel 12 to circulate a circulating fluid for exchanging heat with a soil; tube fitting members 21, 24 provided in a flange part or a web part of the H-shape steel 12 and having a holding part for holding the soil heat exchanging tube 23; and a protective member 25 provided at the lower end of the H-shape steel 12 or in the vicinity of the lower end to cover the lower side of the groove space provided with the soil heat exchanging tube, thereby protecting the soil heat exchanging tube when the H-shape steel and the soil heat exchanging tube are inserted in soil cement before solidification.