Hydrocarbon oil obtained by Fischer-Tropsch (FT) synthesis reaction using a catalyst within a slurry bed reactor is fractionated into a distilled oil and a column bottom oil in a rectifying column, part of the column bottom oil is flowed into a first transfer line that connects a column bottom of the rectifying column to a hydrocracker, at least part of the column bottom oil is flowed into a second transfer line branched from the first transfer line and connected to the first transfer line downstream of the branching point, the amount of the catalyst fine powder to be captured is monitored while the catalyst fine powder in the column bottom oil that flows in the second transfer line are captured by a detachable filter provided in the second transfer line, and the column bottom oil is hydrocracked within the hydrocracker.