To provide a hydrotreating method of gas oil capable of manufacturing a high quality low sulfur gas oil effectively.

This hydrotreating system of gas oil for hydrotreating a charge gas oil LGO comprises a first hydrotreating unit 10 for hydrotreating the charge gas oil LGO, a second hydrotreating unit 20 for hydrotreating a first product oil obtd. from the first hydrotreating unit 10, and a fractionator 30 for separating a second product oil obtd. from the second hydrotreating unit 20 into a light fraction and a heavy fraction. A high quality low sulfur gas oil is effectively manufactured by charging a part of the heavy fraction again to the second hydrotreating unit 20 with the first product oil, and blending the other part of the heavy fraction to the light fraction to make this desulfurized gas oil DGO.