In the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication determines to stop the D2D communication and transmits information indicating the stop of the D2D communication to a terminal with which the user terminal communicates.

In the first embodiment and the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication performs negotiation between terminals such that a radio resource used in a D2D terminal group including the user terminal is different from a radio resource used in a D2D terminal group including the another user terminal.

In the first embodiment and the second embodiment, in response to the detection of interference to the D2D communication from another user terminal, the user terminal performing the D2D communication changes a radio resource used in the D2D communication to another radio resource.

In the first embodiment and the second embodiment, the user terminal, which changes the radio resource used in the D2D communication to the another radio resource, broadcasts change information indicating a change to the another radio resource by using the another radio resource.

In the second embodiment, when another user terminal, which belongs to a D2D terminal group different from the D2D terminal group including the user terminal, receives the change information during the use of the another radio resource, the another user terminal notifies a serving cell of the another user terminal of the reception of the change information.