A gas turbine engine system is provided which achieves high efficiency while using sunlight as a heat source. In a gas turbine engine system including: a compressor configured to compress a first working medium; a heater configured to heat the compressed first working medium by an external heat source; a turbine configured to output power from the first working medium; and an intermediate cooler provided at the compressor and configured to cool the first working medium compressed by a low-pressure compression part of the compressor and supply the first working medium to a high-pressure compression part of the compressor, an organic Rankine cycle engine using, as a second working medium, an organic substance which is a cooling medium of the intermediate cooler is provided.