To provide an underground heat utilization heat pump system increasing the heat exchange quantity of an underground heat exchange well by burying an exchange well heat exchange quantity increasing means adjacently to a circulating pipeline body in the underground heat exchange well.

The underground heat utilization heat pump system includes the underground heat exchange well 2 excavated in the ground; a first circulating pipeline body A buried in the underground heat exchange well 2 to form an underground heat side heat exchange part 3 and to allow a first circulating fluid to circulate; a second circulating pipeline body B having a load side heat exchange part 29 for heating or cooling a thermal control object and allowing a second circulating fluid to circulate; an underground heat utilization heat pump 6 provided between the first circulating pipeline body A and the second circulating pipeline body B to produce the second circulating fluid higher or lower in temperature than the first circulating fluid; and the exchange well heat exchange quantity increasing means buried adjoining the underground heat side heat exchange part 3 in the underground heat exchange well 2 to increase the heat exchange quantity of the underground heat exchange well 2. The exchange well heat exchange quantity increasing means is preferably a U-shaped pipeline body 15 formed with holes on one side.