A user equipment in a radio communication system supporting D2D communication includes a determination unit that receives a first region in a radio frame, which is commonly used for downlink communication and uplink communication with a base station and includes the first region to which a downlink pilot signal and a downlink control signal are to be mapped and a second region to which downlink user data or uplink data is to be mapped, to determine whether a D2D signal is transmittable using the second region; and a transmission unit that transmits the D2D signal using the second region in the radio frame where a D2D physical control channel and a D2D physical data channel are time-multiplexed when the determination unit determines that the D2D signal is transmittable.