PROBLEM TO BE SOLVED: To provide a fuel oil base material obtainable from a heavy fraction obtainable by fractionating thermal decomposition oil.SOLUTION: Provided is a fuel oil base material obtainable by fractionating decomposed oil obtainable, using a flow catalytic decomposition apparatus, by decomposing raw material oil including heavy fraction obtainable by fractionating heat decomposition oil obtained by subjecting naphtha to heat decomposition.