A producing method of monocyclic aromatic hydrocarbons from the oil feedstock having a 10 volume % distillation temperature of more than or equal to 140° C. and a 90 volume % distillation temperature of less than or equal to 380° C. by bringing into contact with an aromatic production catalyst includes the steps of: introducing the oil feedstock into a cracking and reforming reaction apparatus housing the aromatic production catalyst; bringing the oil feedstock and the aromatic production catalyst into contact with each other at the inside of the cracking and reforming reaction apparatus; heating the oil feedstock in advance before introducing the oil feedstock into the cracking and reforming reaction apparatus and forming a two-phase gas-liquid stream; separating the two-phase gas-liquid stream into a gas fraction and a liquid fraction; and introducing the gas fraction and the liquid fraction at different positions of the cracking and reforming reaction apparatus.