To prevent wasteful use of resources by preventing a target base station from transmitting a packet of the outside of the range of the reception window of a PDCP layer set to a user device in the case where the target base station transmits packets to the user device on the basis of a PDCP status report transmitted by the user device having performed inter-base station handover.

A target side base station includes: an inter-base station communication unit which receives a notification signal of a start sequence number which is a first sequence number added to a packet to be transmitted to a user device from a source side base station; and a radio communication unit which receives a status report signal indicating whether the user device was able to receive the packet or not from the user device. Even if the status report signal indicates that the packet with the start sequence number was able to be received, the radio communication unit transmits the packet with the start sequence number to the user device and makes the reception window of the user device start with the next of the start sequence number.