To dehydrogenate ethylbenzene into styrene in improved production efficiency without using many reaction devices and preheaters by passing the ethylbenzene through one or more dehydrogenation reaction pipes each charged with a dehydrogenation catalyst under a specific condition.

This method for hydrogenating ethylbenzene into styrene comprises passing the ethylbenzene through one or more dehydrogenation reaction pipes 16 each charged with a dehydrogenation catalyst, adding heat to the reaction pipes along their longitudinal substantial parts, and increasing the heating along the reaction pipes 16 toward the flow of the passing raw material to change the quantity of the heat added to the reaction pipes 16. Thus, the single small catalyst reaction device of non-adiabatic, non-isothermal and virtually increasingly heating type is used.