An apparatus and method for constructing a data unit that includes a buffer status report (BSR) such that when BSR triggering is performed, the size(s) of the necessary sub-header(s) are also to be considered together in addition to the BSR size. There is a checking unit that checks whether any padding region is available in a MAC PDU that was constructed, a comparing unit that compares the number of padding bits with the size of a buffer status report (BSR) plus its sub-header, and a processing unit that cooperates with the checking unit and the comparing unit to trigger a buffer status report (BSR) procedure if the number of padding bits is larger than the size of the BSR plus its sub-header, including the BSR and its sub-header in the MAC PDU, and setting an LCID in the sub-header to indicate a BSR is included, the BSR having been triggered due to padding. Using such apparatus allows the sub-header(s) to be inserted (included) into the MAC PDU (or transport block (TB) or other data unit).