To provide a geothermal heat pump device enabling totally efficient operation by optimally collecting underground heat.

During load operation, a control means 18 increases the rotational frequency of a geothermal circulating pump 11 when a temperature gradient of heating medium temperature detected by an underground going temperature detection means 12 or an underground return temperature detection means 13 is a downward pitch, and reduces the rotational frequency of the geothermal circulating pump 11 when the temperature gradient of the heating medium temperature detected by the underground going temperature detection means 12 or the underground return temperature detection means 13 is an upward pitch. Thus, the magnitude of changing load and the underground state can be recognized by the underground going temperature detection means 12 or the underground return temperature detection means 13, and the rotational frequency of the geothermal circulating pump 11 can be set so as to achieve a circulation flow rate to secure heat collection amount necessary for the load. As a result, without causing excessive heat collection and shortage of heat collection, optimal heat collection can be achieved, so as to improve the total efficiency of the geothermal heat pump device.