1. A user equipment having a function of device-to-device (D2D) communication, comprising:a controller configured to determine whether the user equipment is in a radio resource control (RRC) idle mode in which no RRC connection is established between the user equipment and a base station, based on whether the user equipment has an RRC connection with the base station;
a receiver configured to receive a system information block (SIB) broadcasted by the base station, in the RRC idle mode of the user equipment, the SIB used to control the D2D communication; and
a transmitter configured to transmit data to other user equipment by the D2D communication based on the SIB, while the user equipment is in the RRC idle mode, wherein
the SIB includes resource information and power information, the resource information indicating usable radio resources for the D2D communication, the power information being used for controlling transmission power in the D2D communication,
the controller determines radio resources used to transmit the data based on the resource information,
the controller determines transmission power used in transmitting the data based on the power information, and
the transmitter transmits the data using the determined radio resources and the determined transmission power.