We carried out experiments attempting to measure thermal conductance of an evaporator with a low-pressure refrigerant, and proposed a model calculation which explained behavior of the measured thermal conductance. Utilizing an apparatus which consisted of heat loads, an evaporator, a heat exchanger, and a chiller, evaporator’s receiving heat at different conditions was measured. The thermal conductance was obtained from relations of the evaporator’s receiving heat to temperature differences between a cold liquid refrigerant and hot air, and it found that the heat receiving performance with the low-pressure refrigerant changed significantly at a specific temperature difference. In order to explain this phenomenon, a model calculation based on the fact that boiling started when vapor pressure of a refrigerant overcame the Laplace pressure was proposed. This understanding of characteristics of evaporator’s heat receiving performance will be important when a refrigeration cycle starts utilizing low-GWP (Global Warming Potential) and low-pressure refrigerants.