A communication method in a roadside unit that acquires first dynamic information indicative of a dynamic object around the roadside unit and second dynamic information indicative of a dynamic object around in-vehicle units includes: selecting at least one in-vehicle unit from among the plurality of in-vehicle units on a basis of a list in which the second dynamic information and the in-vehicle units having the second dynamic information are associated with each other; acquiring the first dynamic information indicative of a state around the roadside unit acquired by a sensor mounted in the roadside unit; configurating a dynamic map on a basis of the acquired first dynamic information, the second dynamic information acquired from the selected in-vehicle unit, and a static map indicative of a static object; and transmitting the dynamic map to one or more of the in-vehicle units that communicate with the roadside unit.