the present invention provides a screw compressor for refrigerating apparatus capable of controlling the rotational speed of a motor to be suitable for cooling heat load by simply controlling an inverter , without causing the overload of the motor . the screw compressor 1 a for refrigerating apparatus 10 a , which uses a motor 22 controlled by an inverter , as a driving portion , is provided with a suction pressure detector d 3 as a heat load detecting means for detecting the cooling heat load ; a motor coil temperature detector d 1 as a means for detecting the load condition of the motor 22 ; and a controller 26 that decreases the rotational speed of the motor 22 if the capacity of the compressor is determined as excessive based on a pressure signal from the detector d 3 , maintains the rotational speed if the capacity is determined neither excessive nor lacking . in case that the capacity is determined as lacking , the controller 26 reduces the rotational speed if the load condition is determined as excessive based on a temperature signal from the detector d 1 and increases the rotational speed in the other case .