. Still further, in accordance with the present invention, there is provided a brine cooling apparatus including a screw compressor, a condenser, a main expansion valve, an evaporator, a pipe for connecting the screw compressor, the condenser, the main expansion valve and the evaporator, a refrigerant evaporated by the evaporator, and brine flowing through the evaporator, the brine being cooled by evaporating the refrigerant by the evaporator. The refrigerant is an ammonia refrigerant, the evaporator is a plate type heat exchanger constructed by stacking a plurality of plates, and suction pressure detecting means for detecting a suction pressure of the compressor