A refrigerant compressor includes a compression mechanism, a discharge passage, and an oil separator. The compression mechanism compresses a refrigerant gas containing a lubricant oil. The refrigerant gas that has been compressed by the compression mechanism flows through the discharge passage. The oil separator is arranged in the discharge passage and separates the lubricant oil from the refrigerant gas flowing in the discharge passage. The oil separator has a rotator that causes the refrigerant gas to flow around the axis of the rotator and a circumferential wall that encompasses the rotator and extends along the axis of the rotator. The rotator and the circumferential wall define a separation zone in between. The lubricant oil is separated from the refrigerant gas by the flow of the refrigerant gas around the rotator in the separation zone. The circumferential wall has an oil outlet that allows the separated lubricant oil to flow to the exterior of the oil separator. The oil separator has an inlet port that allows the refrigerant gas to flow into the separation zone and an outlet port that allows the refrigerant gas to flow out of the separation zone. The rotator is arranged between the inlet port and the outlet port. The inlet port and the outlet port are arranged so that an inlet direction of the refrigerant gas flowing through the inlet port is substantially parallel with an outlet direction of the refrigerant gas flowing through the outlet port.