A gas compressor comprising: a block part inside which a cylinder chamber is formed; a rotor rotatably housed in the cylinder chamber; and a plurality of vanes provided in an outer circumferential portion of the rotor at an interval in a circumferential direction of the rotor, the vanes being capable of emerging from the outer circumferential portion, an inner circumferential surface of the cylinder chamber, an outer circumferential surface of the rotor, and each two of the vanes adjacent in the circumferential direction of the rotor defining a compression chamber inside the cylinder chamber, the block part having a pressure supply part configured to supply pressure to backpressure spaces formed behind the respective vanes, wherein the pressure supply part has an intermediate-pressure supply part (51, 67) which communicates with each backpressure space from an intake cycle to a compression cycle in the compression chamber, a first high-pressure supply part (53, 69) which communicates with the backpressure space from the compression cycle to a discharge cycle in the compression chamber, and the gas compressor is characterized by the pressure supply part having a second high-pressure supply part which is formed between the intermediate-pressure supply part and the first high-pressure supply part independently of the first high-pressure supply part and which communicates with the backpressure space in a middle of the compression cycle in the compression chamber. a block part inside which a cylinder chamber is formed; a rotor rotatably housed in the cylinder chamber; and a plurality of vanes provided in an outer circumferential portion of the rotor at an interval in a circumferential direction of the rotor, the vanes being capable of emerging from the outer circumferential portion, an inner circumferential surface of the cylinder chamber, an outer circumferential surface of the rotor, and each two of the vanes adjacent in the circumferential direction of the rotor defining a compression chamber inside the cylinder chamber, the block part having a pressure supply part configured to supply pressure to backpressure spaces formed behind the respective vanes, wherein the pressure supply part has an intermediate-pressure supply part (51, 67) which communicates with each backpressure space from an intake cycle to a compression cycle in the compression chamber, a first high-pressure supply part (53, 69) which communicates with the backpressure space from the compression cycle to a discharge cycle in the compression chamber, and the gas compressor is characterized by the pressure supply part having a second high-pressure supply part which is formed between the intermediate-pressure supply part and the first high-pressure supply part independently of the first high-pressure supply part and which communicates with the backpressure space in a middle of the compression cycle in the compression chamber. an intermediate-pressure supply part (51, 67) which communicates with each backpressure space from an intake cycle to a compression cycle in the compression chamber, a first high-pressure supply part (53, 69) which communicates with the backpressure space from the compression cycle to a discharge cycle in the compression chamber, and the gas compressor is characterized by the pressure supply part having a second high-pressure supply part which is formed between the intermediate-pressure supply part and the first high-pressure supply part independently of the first high-pressure supply part and which communicates with the backpressure space in a middle of the compression cycle in the compression chamber.