To convey a refrigerant under low power with high reliability while the refrigerant is controlled and lubricating oil is ensured with ease.

A sub-refrigerant is condensed by one sub-heat exchanger 43 or 44 of two sub-heat exchangers 43 and 44 and the sub-refrigerant is evaporated by the other sub-heat exchanger 43 or 44, so that the thermal energy of a refrigerating circuit 40 is converted into refrigerant conveying force to circulate the main refrigerant of a main refrigerant circuit 20. Thus, since the main refrigerant is conveyed under the thermal energy, a high operation can be performed with high reliability under low power.