NOVELTY - The hydrocarbon oil (C) is obtained by hydrodesulfurizing a hydrocarbon mixture having preset properties, at specific conditions, using nickel-tungsten, nickel-molybdenum, cobalt-molybdenum, cobalt-tungsten or nickel-cobalt-molybdenum catalyst. Specific amount of light oil and linear saturated hydrocarbons are removed from the obtained hydrodesulfurization processed oil, to obtain hydrocarbon oil having specific properties.    USE - For hydrogen production in hydrogen-production system (claimed).    ADVANTAGE - The hydrocarbon oil has high degree of desulfurization and enables reformer to have excellent durability. The hydrocarbon oil provides reformed gases having reduced carbon monoxide content, and has high hydrogen generation efficiency.    DETAILED DESCRIPTION - The hydrocarbon oil (C) is obtained using a hydrocarbon mixture as raw material oil. The hydrocarbon mixture has initial boiling point of 140-180degreesC, 90 volume% distillation temperature of 200-270degreesC, aromatic content of 20 volume% or less, linear saturated-hydrocarbon content of 25 mass% or more, 10-15C linear saturated-hydrocarbon content of 20 mass% or more and sulfur content of 300 mass ppm or less. The hydrocarbon oil is obtained by performing hydro desulfurization processing of the raw material oil, at hydrogen pressure of 5-10 MPa, LHSV of 0.5-3 hour-1, hydrogen/hydrocarbon capacitance ratio of 0.15-0.6 and reaction temperature of 250-310degreesC, using nickel-tungsten, nickel-molybdenum, cobalt-molybdenum, cobalt-tungsten or nickel-cobalt-molybdenum catalyst. 1-35 volume% of light oil is removed from the obtained hydrodesulfurization processed oil, followed by removing 10 volume% or more of linear saturated hydrocarbons using zeolite at 150-250degreesC and at 1-5 MPa. The obtained hydrocarbon oil has initial boiling point of 160-200degreesC, 50 volume% distillation temperature of 200-220degreesC, 90 volume% distillation temperature of 200-245degreesC, aromatic content of 10 volume% or less, sulfur content of 0.5 mass ppm or less, naphthene content of 40 volume% or more, oxidation initial temperature of 210degreesC or more and 13C hydrocarbon content of 20 mass% or more. An INDEPENDENT CLAIM is included for the hydrogen-production system. The hydrogen-production system consists of a desulfurizer (E) in which reaction pressure is maintained at less than 1 MPa. The desulfurizer controls and de-sulfurizes the hydrocarbon oil, using desulfurization-catalyst layer, at a temperature range between (initial boiling point temperature of hydrocarbon oil -50degreesC) to (initial boiling point temperature of hydrocarbon oil +100degreesC).    DESCRIPTION OF DRAWING(S) - The figure shows the flowchart of the evaluation system containing desulfurizer.    tank (A)    balance (B)    hydrocarbon oil (C)    pump (D)    desulfurizer (E)