An on-vehicle communication device capable of suppressing a delay in providing information, avoiding congestion, and sufficiently securing transmission power, includes a communication controller to controls a transmission cycle and transmission power when data is transmitted from a transmitting/receiving device. The communication controller uses its own vehicle information and surrounding vehicle information to estimate a degree of risk and a safe distance of its own vehicle. The communication controller controls the transmission cycle of its own vehicle based on a communication channel utilization rate of its own vehicle, a communication channel utilization rate of a surrounding vehicle and the degree of risk of its own vehicle, and controls the transmission power of its own vehicle based on the communication channel utilization rate of its own vehicle, the communication channel utilization rate of the surrounding vehicle and the safe distance.