Refrigerant cycle apparatus

For a purpose of preventing a compressor (11) from being damaged by liquid compression without disposing any accumulator on a low-pressure side, there is disclosed a transition critical refrigerant cycle apparatus having a supercritical pressure on a high-pressure side. The transition critical refrigerant cycle apparatus constituted by connecting a compressor (11), a gas cooler (12), a pressure reducing device (14), an evaporator (15) and the like in an annular shape, using carbon dioxide as a refrigerant, and capable of having the supercritical pressure on the high-pressure side comprises: an internal heat exchanger (45) for exchanging heat between a refrigerant which has flown out of the gas cooler (12) and a refrigerant which has flown out of the evaporator (15). This internal heat exchanger (45) comprises a high-pressure-side channel (64) through which the refrigerant from the gas cooler (12) flows, and a low-pressure-side channel (66) which is disposed in a heat exchanging manner with this high-pressure-side channel (64) and through which the refrigerant from the evaporator (15) flows, the refrigerant is passed upwards from below in the high-pressure-side channel (64), and the refrigerant is passed downwards from above in the low-pressure-side channel (66).