A base station comprising: an obtaining section configured to obtain a Medium Access Control, MAC, Protocol Data Unit, PDU; and a transmission processing section configured to transmit the MAC PDU in downlink, wherein the MAC PDU includes a plurality of identifiers and beam related information corresponding to each of one or more identifiers included in the plurality of identifiers and does not include beam related information corresponding to another identifier included in the plurality of identifiers, in order to allow a terminal apparatus to obtain beam related information corresponding to an identifier used for the terminal apparatus out of the plurality of identifiers in a case where the identifier used for the terminal apparatus is included in the one or more identifiers, the MAC PDU further includes a MAC header, the MAC header includes a first region in which the plurality of identifiers is arranged and a second region in which the beam related information corresponding to each of the one or more identifiers is arranged, the one or more identifiers are arranged ahead of the another identifier in the first region, the MAC PDU includes data corresponding to each of the plurality of identifiers and a MAC payload, and the MAC payload includes a data region in which the data corresponding to each of the plurality of identifiers is arranged. an obtaining section configured to obtain a Medium Access Control, MAC, Protocol Data Unit, PDU; and a transmission processing section configured to transmit the MAC PDU in downlink, wherein the MAC PDU includes a plurality of identifiers and beam related information corresponding to each of one or more identifiers included in the plurality of identifiers and does not include beam related information corresponding to another identifier included in the plurality of identifiers, in order to allow a terminal apparatus to obtain beam related information corresponding to an identifier used for the terminal apparatus out of the plurality of identifiers in a case where the identifier used for the terminal apparatus is included in the one or more identifiers, the MAC PDU further includes a MAC header, the MAC header includes a first region in which the plurality of identifiers is arranged and a second region in which the beam related information corresponding to each of the one or more identifiers is arranged, the one or more identifiers are arranged ahead of the another identifier in the first region, the MAC PDU includes data corresponding to each of the plurality of identifiers and a MAC payload, and the MAC payload includes a data region in which the data corresponding to each of the plurality of identifiers is arranged. the MAC PDU further includes a MAC header, the MAC header includes a first region in which the plurality of identifiers is arranged and a second region in which the beam related information corresponding to each of the one or more identifiers is arranged, the one or more identifiers are arranged ahead of the another identifier in the first region, the MAC PDU includes data corresponding to each of the plurality of identifiers and a MAC payload, and the MAC payload includes a data region in which the data corresponding to each of the plurality of identifiers is arranged.