A compact heat pump system and a heat pump operation method employs an evaporator for recovering heat of an external heat source to a working medium supplied as liquid water from the exterior via a water feed channel, thereby evaporating the working medium, a compressor for compressing the working medium evaporated in the evaporator and increasing temperature of the evaporated working medium, and a driving unit for giving motive power to drive the compressor. The heat pump system further includes a supply channel for supplying, as a heat source, vapor of the working medium having a temperature increased by the compressor to an external heat-utilizing facility, and a return channel branched from the supply channel and introducing the working medium discharged from the compressor to the evaporator.