A refrigeration system including a scroll type compressor having a stationary scroll member, an orbiting scroll member, a discharge port formed in the central portion of the end plate of the fixed scroll member, a suction port formed in a peripheral portion of the fixed scroll member, and at least one gas injection port formed through the thickness of an end plate of the fixed scroll member in a portion of the end plate near the spiral wrap, at a position spaced from the wall of the spiral wrap by a radial distance less than the thickness of the spiral wrap. A discharge pipe is connected to the discharge port, with a suction pipe being connected to the suction port. A refrigerant circuit is connected between the suction pipe and the discharge pipe of the scroll type compressor and includes a four-way valve, indoor heat exchanger, first pressure reducer, gas-liquid separator, second pressure reducer and an outdoor heat exchanger. A gas injection passage is connected between the gas outlet formed in an upper part of the gas-liquid separator and the gas injection port, so as to permit the refrigerant gas in the upper part of the gas-liquid separator to be additionally supplied into the compression chambers under compression in the scroll type compressor.