Refrigeration cycle control unit

A refrigeration cycle control unit comprises a discharge pressure estimation means for estimating a discharge pressure of a compressor (18) by referring to a physical value with a correlation with a suction pressure of the compressor (18) estimated or detected by a suction pressure estimation or detection means and a physical value with a correlation with a pressure difference between the discharge pressure and the suction pressure estimated or detected by a pressure difference estimation or detection means. In a refrigeration cycle having an external signal control type variable displacement compressor (18), a discharge pressure of the compressor (18) can be estimated without detecting a high-pressure side pressure by a sensor, and the discharge pressure can be controlled at an optimum pressure to protect the compressor (18), and further, it is possible to make a more inexpensive system.