PURPOSE: To eliminate the necessity of an external balance line by providing an oil pressure regulator and low oil pressure indicator for regulating and also monitoring the pressure in an oil pump to distribute the oil in the crank chamber of a compressor to the lubrication potions of the compressor linking in the operation of a refrigerant compressor.

CONSTITUTION: This pressure regulator 10 combined with a low pressure indicator is provided in the bore 12 of a housing 14 relating an oil pump 16 and refrigerant compressor 18 and has a narrow cylindrical regulator housing 28. This housing 28 is given a step from a threaded section 36 toward a smaller diameter section 38 than the bore 12, forming a chamber 41 communicating with the bore 12 through an oil leakage passage 24 and the crank chamber 22 of the compressor 18. The regulator 10 has thin and long electrically conductive piston 56, which is fitted to the inner diameter section 48 of the housing 28. The largest diameter section 74 of the piston 56 is fitted to the largest inner diameter section 50 of the housing 28 and is energized to the side of a electrically conductive member 104 by a spring 50.