Disclosed are a device and a method for continuously polymerizing polybutene by removing halogen acid, which is included in a reaction raw material, by adsorbing the halogen acid using an adsorbent and then re-supplying the reaction raw material into a reactor. The device for re-circulating the raw material when manufacturing polybutene comprises a reactor, into which a catalyst and a reaction raw material (diluted with an inactive organic solvent) are supplied and polymerized to produce a reaction product; a neutralizing/washing tank for removing the catalyst from the reaction product and neutralizing the reaction product; a separation tank for separating the reaction product into organic compounds and water; a C4 distillation column for distilling an unreacted raw material and the inactive organic solvent from the organic compounds; and an impurity adsorption column for removing halogen acid from the distilled unreacted raw material and the inactive organic solvent using an adsorbent.