Provided is a process for adsorptive separation of p-xylene from an aromatic hydrocarbon mixture comprising other isomers of xylene, and a device used therein. More specifically, the present invention provides a separation process employing simulated moving bed (SMB) adsorptive chromatography, characterized by pretreating a fluid mixture, i.e. the feed, by using single adsorption chamber so as to raise the concentration of a component to be separated, and then carrying out the simulated moving bed adsorptive separation, thereby improving productivity, and a device used therein.