A user apparatus is described that performs D2D communication by radio, including a signal reception unit configured to detect a signal addressed to the user apparatus by detecting an identifier of a physical layer of the user apparatus that is associated with an identifier of an upper layer of the user apparatus from a signal received by radio. The signal reception unit further detects data of the upper layer addressed to the user apparatus by using the identifier of the physical layer of the user apparatus as a part of the identifier of the upper layer of the user apparatus.