An image decoding method performed by a decoding device according to the present document comprises the steps of: obtaining image information including an output layer set (OLS) decoded picture buffer (DPB) parameter index for a target OLS and DPB parameter information; deriving DPB parameter information for the target OLS on the basis of the OLS DPB parameter index; performing a picture management process on pictures of a DPB on the basis of the DPB parameter information for the target OLS; configuring a reference picture list for a current picture on the basis of the pictures of the DPB; and performing an inter prediction on a block in the current picture on the basis of the reference picture list.