A variable heat/power ratio cogeneration system comprising: a gas turbine that uses gasification gas obtained by gasifying a solid or liquid fuel and a normal fuel that is natural gas, oil gas, or light fuel oil, the normal fuel being used as an alternative or auxiliary fuel when the gas turbine is start-up and stopped or when the amount of the gasification gas to be supplied is small; a combustor that combusts the gasification gas and the normal fuel to generate combustion gas; a heat recovery steam generator that uses exhaust gas of the gas turbine to generate steam; a process system that supplies the generated steam to a steam consumption facility; a steam system that injects extra steam into the gas turbine, characterized by the steam system including a first steam system that injects the extra steam on the upstream side of a flame zone with respect to the flow of the combustion gas in the combustor and a second steam system that is branched from the first steam system and injects the extra steam on the downstream side of the flame zone with respect to the flow of the combustion gas in the combustor; a first steam flow rate control valve that is arranged in the first steam system and capable of controlling the flow rate of the steam to be injected by the first steam system; a second steam flow rate control valve that is arranged in the second steam system and capable of controlling the flow rate of the steam to be injected by the second steam system; a gasification gas flow rate detector that detects the flow rate of the gasification gas; a normal fuel flow rate detector that detects the flow rate of the normal fuel; a demanded steam amount detector that detects a demanded amount of steam necessary for the steam consumption facility; and a controller that acquires the flow rate of the gasification gas detected by the gasification gas flow rate detector and the flow rate of the normal fuel detected by the normal fuel flow rate detector to control the first steam flow rate control valve on the basis of signals indicating the acquired flow rates, the controller further acquiring the demanded steam amount detected by the demanded steam amount detector and necessary for the steam consumption facility to control the second steam flow rate control valve on the basis of a signal indicating the demanded steam amount. a gas turbine that uses gasification gas obtained by gasifying a solid or liquid fuel and a normal fuel that is natural gas, oil gas, or light fuel oil, the normal fuel being used as an alternative or auxiliary fuel when the gas turbine is start-up and stopped or when the amount of the gasification gas to be supplied is small; a combustor that combusts the gasification gas and the normal fuel to generate combustion gas; a heat recovery steam generator that uses exhaust gas of the gas turbine to generate steam; a process system that supplies the generated steam to a steam consumption facility; a steam system that injects extra steam into the gas turbine, characterized by the steam system including a first steam system that injects the extra steam on the upstream side of a flame zone with respect to the flow of the combustion gas in the combustor and a second steam system that is branched from the first steam system and injects the extra steam on the downstream side of the flame zone with respect to the flow of the combustion gas in the combustor; a first steam system that injects the extra steam on the upstream side of a flame zone with respect to the flow of the combustion gas in the combustor and a second steam system that is branched from the first steam system and injects the extra steam on the downstream side of the flame zone with respect to the flow of the combustion gas in the combustor; a first steam flow rate control valve that is arranged in the first steam system and capable of controlling the flow rate of the steam to be injected by the first steam system; a second steam flow rate control valve that is arranged in the second steam system and capable of controlling the flow rate of the steam to be injected by the second steam system; a gasification gas flow rate detector that detects the flow rate of the gasification gas; a normal fuel flow rate detector that detects the flow rate of the normal fuel; a demanded steam amount detector that detects a demanded amount of steam necessary for the steam consumption facility; and a controller that acquires the flow rate of the gasification gas detected by the gasification gas flow rate detector and the flow rate of the normal fuel detected by the normal fuel flow rate detector to control the first steam flow rate control valve on the basis of signals indicating the acquired flow rates, the controller further acquiring the demanded steam amount detected by the demanded steam amount detector and necessary for the steam consumption facility to control the second steam flow rate control valve on the basis of a signal indicating the demanded steam amount.