Mobile station with packet reordering function

A mobile station that performs sequenced delivery of packets received from base stations based on sequence numbers, comprising: receiving means (31) for receiving a first packet data convergence protocol (PDCP) protocol data unit (PDU) from a source base station (11a) and a second PDCP PDU from a target base station ( 11b), the second PDCP PDU including a sequence number that was transmitted via a control plane from the source base station (11a) to the target base station (llb); storage means (32) for storing the PDCP SDUs corresponding to the first PDCP PDU and the second PDCP PDU; and reordering means for performing sequential delivery of the stored PDCP SDUs by reordering the first PDCP PDU and the second PDCP PDU using the sequence numbers that are attached to the first PDCP PDU and the second PDCP PDU.