A protecting device for protecting a refrigerant compressor from overheating or seizure caused by a shortage of refrigerant by any chance such as leakage thereof. The device includes a temperature sensor disposed on the outer wall of the compressor casing in the vicinity of a refrigerant intake suction suction port for sensing the temperature of the outer wall to output the sensed or measured data and a discriminator for discriminating an occurrence of refrigerant shortage by an excess of the data over a predetermined condition for comparison. The signals from the discriminator cause a warning issuance of the refrigerant shortage or an automatic stoppage of the compressor operation.