Heavy oil containing not greater than 12 wt% of hydrogen as a raw material oil is subjected to solvent extraction, so that the hydrogen content increases by 0.2 wt% or more with respect to the raw material oil. After this, hydrotreating is performed so that the hydrogen content increases by 0.5 wt% or more with respect to the extraction oil, thereby obtaining refined oil. Thus, it is possible to obtain refined oil by using cheap heavy oil as a raw material and by using a simple and reliable method.
