A method and device for supporting a hybrid automatic repeat request (HARQ) in an unlicensed band is provided. A user equipment receives first downlink control information (DCI) including uplink scheduling information. The first DCI further includes a carrier indicator field (CIF) indicating a cell to be scheduled. If the type of the cell indicated by the CIF is a licensed cell, the format of the DCI is determined as a first DCI format including a first resource allocation (RA) field used for the uplink scheduling information. If the type of the cell indicated by the CIF is an unlicensed cell, the format of the DCI is determined as a second DCI format including a second RA field used for the uplink scheduling information.