A radio communication system including a user equipment and a base station, the user equipment comprising: a transmission and reception unit configured to transmit and receive a radio signal to and from a base station; and a buffer status report transmission unit configured to transmit, to the base station, a speculative buffer status report indicating a buffer status that is expected in a subsequent subframe, wherein the transmission and reception unit is configured to transmit to the base station a scheduling request and, when receiving an uplink grant with respect to the scheduling request from the base station, the buffer status report transmission unit is configured to, with regard to a current subframe k, conduct an expectation of a size of transmission target data, which remains in a buffer in a subsequent subframe k+N after N subframes from the current subframe k, and configured to transmit to the base station the data size which is expected as the speculative buffer status report, wherein the subsequent subframe k+N, which is indicated in the speculative buffer status report, is a subframe after a predetermined number of subframes N from the current subframe k in which the speculative buffer status report is transmitted, or a subframe after a number of subframes N, which is indicated in the speculative buffer status report, from the current subframe k, wherein, the base station is configured to when reaching the subframe k+N, virtually regard that a buffer status report is received in the subframe k+N, in accordance with the speculative buffer status report that is received in the subframe k, and configured to transmit an uplink grant to the user equipment on the basis of the data size shown in the speculative buffer status report. a transmission and reception unit configured to transmit and receive a radio signal to and from a base station; and a buffer status report transmission unit configured to transmit, to the base station, a speculative buffer status report indicating a buffer status that is expected in a subsequent subframe, wherein the transmission and reception unit is configured to transmit to the base station a scheduling request and, when receiving an uplink grant with respect to the scheduling request from the base station, the buffer status report transmission unit is configured to, with regard to a current subframe k, conduct an expectation of a size of transmission target data, which remains in a buffer in a subsequent subframe k+N after N subframes from the current subframe k, and configured to transmit to the base station the data size which is expected as the speculative buffer status report, wherein the subsequent subframe k+N, which is indicated in the speculative buffer status report, is a subframe after a predetermined number of subframes N from the current subframe k in which the speculative buffer status report is transmitted, or a subframe after a number of subframes N, which is indicated in the speculative buffer status report, from the current subframe k, wherein, the base station is configured to when reaching the subframe k+N, virtually regard that a buffer status report is received in the subframe k+N, in accordance with the speculative buffer status report that is received in the subframe k, and configured to transmit an uplink grant to the user equipment on the basis of the data size shown in the speculative buffer status report.