Gas-turbine power generating installation and method of operating the same

A gas-turbine power generating installation capable of effectively utilizing gases produced in overage gas fields, etc. and a method of operating the installation are provided. The gas-turbine power generating installation (10) is installed in the vicinity of an outrage gas field or an oil field. In the installation, air compressed by a compressor (1) is introduced to a combustor (2) for combustion after being mixed with fuel, a gas turbine (3) is driven by generated combustion gas, and a power generator (5) is driven by motive power obtained from a rotary shaft of the gas turbine (3). A boosting compressor (6) is driven by the motive power obtained from the rotary shaft of the gas turbine (3), whereby natural gas or accompanying gas is boosted in pressure and supplied as fuel to the combustor (2). The gas turbine (3) generates electric power by using natural gas produced in the outrage gas field or accompanying gas produced in the oil field, and the generated electric power is supplied to a consuming site.