Disclosed are a base station device and a user terminal that provide a favourable search space in a communication system which expands bandwidth by gathering a plurality of basic frequency blocks. A base station device (20) comprises: a selection unit (302) which selects a single basic frequency block from the system band; a downlink control information generation unit (306) which generates downlink control information for demodulating a data channel transmitted discretely on the selected basic frequency block, and provides a search space with aggregated downlink control information for a plurality of basic frequency blocks on a downlink control channel of a designated basic frequency block among the plurality of basic frequency blocks; and a transmission means (203) which transmits on the downlink control channel provided in the aggregated downlink control information in the search space.
