A refrigeration apparatus comprising: a refrigerant circuit including a compression mechanism, a utilization-side heat exchanger, a first expansion valve, a gas-liquid separator, a second expansion valve, and a heat-source-side heat exchanger which are sequentially connected together to perform a two-stage expansion refrigeration cycle, wherein the refrigerant circuit further includes: a gas injection pipe through which gas refrigerant in the gas-liquid separator flows into a portion of the compression mechanism in which refrigerant is being compressed, and a liquid-gas heat exchanger configured to exchange heat between gas refrigerant obtained by evaporating refrigerant in the heat-source-side heat exchanger and travelling toward the compression mechanism and liquid refrigerant travelling from the gas-liquid separator toward the second expansion valve; characterised in that the refrigeration apparatus further comprises an intermediate pressure setter configured to determine an intermediate pressure value of the two-stage expansion refrigeration cycle by modifying a temporary intermediate pressure value until a liquid-to-gas temperature difference between liquid refrigerant and gas refrigerant in the liquid-gas heat exchanger is greater than or equal to a required liquid-to-gas temperature difference determined based on a required degree of superheat of refrigerant sucked into the compression mechanism, where the required degree of superheat is available from a prestored correspondence between superheat and required heating capacity of the utilization-side heat exchanger, and such that an amount of gas refrigerant through the gas injection pipe is greatest; and a valve controller configured to control at least one of the first or second expansion valve or such that an intermediate pressure of the two-stage expansion refrigeration cycle is equal to the intermediate pressure value determined by the intermediate pressure setter. a refrigerant circuit including a compression mechanism, a utilization-side heat exchanger, a first expansion valve, a gas-liquid separator, a second expansion valve, and a heat-source-side heat exchanger which are sequentially connected together to perform a two-stage expansion refrigeration cycle, wherein the refrigerant circuit further includes: a gas injection pipe through which gas refrigerant in the gas-liquid separator flows into a portion of the compression mechanism in which refrigerant is being compressed, and a liquid-gas heat exchanger configured to exchange heat between gas refrigerant obtained by evaporating refrigerant in the heat-source-side heat exchanger and travelling toward the compression mechanism and liquid refrigerant travelling from the gas-liquid separator toward the second expansion valve; characterised in that the refrigeration apparatus further comprises an intermediate pressure setter configured to determine an intermediate pressure value of the two-stage expansion refrigeration cycle by modifying a temporary intermediate pressure value until a liquid-to-gas temperature difference between liquid refrigerant and gas refrigerant in the liquid-gas heat exchanger is greater than or equal to a required liquid-to-gas temperature difference determined based on a required degree of superheat of refrigerant sucked into the compression mechanism, where the required degree of superheat is available from a prestored correspondence between superheat and required heating capacity of the utilization-side heat exchanger, and such that an amount of gas refrigerant through the gas injection pipe is greatest; and a valve controller configured to control at least one of the first or second expansion valve or such that an intermediate pressure of the two-stage expansion refrigeration cycle is equal to the intermediate pressure value determined by the intermediate pressure setter. a gas injection pipe through which gas refrigerant in the gas-liquid separator flows into a portion of the compression mechanism in which refrigerant is being compressed, and a liquid-gas heat exchanger configured to exchange heat between gas refrigerant obtained by evaporating refrigerant in the heat-source-side heat exchanger and travelling toward the compression mechanism and liquid refrigerant travelling from the gas-liquid separator toward the second expansion valve; characterised in that the refrigeration apparatus further comprises an intermediate pressure setter configured to determine an intermediate pressure value of the two-stage expansion refrigeration cycle by modifying a temporary intermediate pressure value until a liquid-to-gas temperature difference between liquid refrigerant and gas refrigerant in the liquid-gas heat exchanger is greater than or equal to a required liquid-to-gas temperature difference determined based on a required degree of superheat of refrigerant sucked into the compression mechanism, where the required degree of superheat is available from a prestored correspondence between superheat and required heating capacity of the utilization-side heat exchanger, and such that an amount of gas refrigerant through the gas injection pipe is greatest; and a valve controller configured to control at least one of the first or second expansion valve or such that an intermediate pressure of the two-stage expansion refrigeration cycle is equal to the intermediate pressure value determined by the intermediate pressure setter.