To provide an onboard communication apparatus which realizes continuous communication with a road antenna without being interrupted by the existence of other vehicles by executing diversity reception with an onboard antenna for receiving a radio wave radiated from the road transmission antenna installed along a road.

This onboard communication apparatus has an onboard communication part 11 and an on-vehicle antenna part 12. The on-vehicle communication part 11 radiates a radio wave containing vehicle data form the onboard antenna part 12 and obtains road traffic data received by the onboard antenna part 12 and contained in the radiated radio wave from the road antenna. When the vehicle 2 passes through a cell, it receives the radio wave from the forward direction or the backward direction of the vehicle 2 or from above when the vehicle 2 passes just below the road antenna. A detection/decoding processing is executed, based on the reception signal. Thus, diversity reception is executed and the influence of interruption by the other vehicle can be avoided.