The hydrocarbon synthesis reaction apparatus is provided with a synthesis gas supply line in which a synthesis gas is compressed and supplied by a first compressor, a reactor configured to accommodate a catalyst slurry, a gas-liquid separator configured to separate an unreacted synthesis gas and hydrocarbons discharged from the reactor into a gas and a liquid, a first recycle line in which the unreacted synthesis gas after separation into a gas and a liquid is compressed and recycled into the reactor by a second compressor, and a second recycle line configured to recycle a residual unreacted synthesis gas after separation into a gas and a liquid into the inlet side of the first compressor at the time of start-up operation when the synthesis gas is gradually increased in the amount to be introduced.