A communication apparatus is installed in a vehicle. A time information obtaining unit obtains a current time. A state information obtaining unit repeatedly obtains state information representing a state of an own vehicle at the current time. An own vehicle information generating unit estimates predicted arrival positions at specific times between the current time and a specified time, and repeatedly generates own vehicle information including the current position and the predicted arrival positions. An information transmitting unit transmits the own vehicle information. An information storage unit stores the own vehicle information into a first storage section as past own vehicle information. The information transmitting unit obtains an information coincidence degree representing the degree of the coincidence between current own vehicle information and the past own vehicle information, and transmits the current own vehicle information if the information coincidence degree is less than a specified threshold.