A producing method of monocyclic aromatic hydrocarbons in which reaction products including monocyclic aromatic hydrocarbons are produced by bringing an oil feedstock and an aromatic production catalyst into contact with each other, 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., the method including the steps of: introducing the oil feedstock into a fluidized-bed reaction apparatus housing the aromatic production catalyst; bringing the oil feedstock and the aromatic production catalyst into contact with each other in the fluidized-bed reaction apparatus; and introducing steam into the fluidized-bed reaction apparatus based on the introducing amount of the oil feedstock per hour.