A process for producing hydrocarbons, said process comprising: a synthesis step of synthesizing hydrocarbons from continuously supplied hydrogen gas and carbon monoxide gas by a Fischer-Tropsch synthesis reaction in presence of a catalyst, a step of discharging light hydrocarbons from a Fischer-Tropsch synthesis reactor, a gas-liquid separation step of separating a light hydrocarbon oil from said light hydrocarbons by cooling the light hydrocarbons, whereby the condensed light hydrocarbon oil is obtained, a step of discharging a slurry containing hydrocarbons and catalyst particles from a Fischer-Tropsch synthesis reactor, a step of separating a heavy hydrocarbon oil from the slurry by filtration, a temporary storage step of continuously supplying said light hydrocarbon oil obtained from said light hydrocarbons to a first buffer tank and said heavy hydrocarbon oil to a second buffer tank, a discharge step of continuously discharging said light hydrocarbon oil and said heavy hydrocarbon oil respectively from said respective buffer tanks, mixing said light hydrocarbon oil and said heavy hydrocarbon oil, and supplying a resulting mixed oil to a fractionator, and a fractional distillation step of fractionally distilling said mixed oil of said light hydrocarbon oil and said heavy hydrocarbon oil into at least a wax fraction and a fraction that is lighter than said wax fraction, wherein estimated production rates for said light hydrocarbon oil and said heavy hydrocarbon oil are respectively determined based on a set reaction temperature in said synthesis step, and discharge flow rates for said light hydrocarbon oil and said heavy hydrocarbon oil in said discharge step are respectively controlled so as to be equal to said respective estimated production rates. a synthesis step of synthesizing hydrocarbons from continuously supplied hydrogen gas and carbon monoxide gas by a Fischer-Tropsch synthesis reaction in presence of a catalyst, a step of discharging light hydrocarbons from a Fischer-Tropsch synthesis reactor, a gas-liquid separation step of separating a light hydrocarbon oil from said light hydrocarbons by cooling the light hydrocarbons, whereby the condensed light hydrocarbon oil is obtained, a step of discharging a slurry containing hydrocarbons and catalyst particles from a Fischer-Tropsch synthesis reactor, a step of separating a heavy hydrocarbon oil from the slurry by filtration, a temporary storage step of continuously supplying said light hydrocarbon oil obtained from said light hydrocarbons to a first buffer tank and said heavy hydrocarbon oil to a second buffer tank, a discharge step of continuously discharging said light hydrocarbon oil and said heavy hydrocarbon oil respectively from said respective buffer tanks, mixing said light hydrocarbon oil and said heavy hydrocarbon oil, and supplying a resulting mixed oil to a fractionator, and a fractional distillation step of fractionally distilling said mixed oil of said light hydrocarbon oil and said heavy hydrocarbon oil into at least a wax fraction and a fraction that is lighter than said wax fraction, wherein estimated production rates for said light hydrocarbon oil and said heavy hydrocarbon oil are respectively determined based on a set reaction temperature in said synthesis step, and discharge flow rates for said light hydrocarbon oil and said heavy hydrocarbon oil in said discharge step are respectively controlled so as to be equal to said respective estimated production rates.