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 subjecting the extracts eluted from a plurality of adsorption chambers arranged in parallel, to a crystallizer for additional separation, thereby improving productivity, and a device used therein.