A route determination device includes a memory to store a piece of route information of the route which is already calculated; and a processor to execute a process including: receiving a calculation request which requests route calculation; determining the route which conforms to the calculation request by performing the route calculation when the route information stored in the memory does not include the route which conforms to the calculation request; obtaining the route which conforms to the calculation request from the route information when the route information stored in the memory includes the route which conforms to the calculation request; storing the route information of the route determined by route determining processing in the memory; and sharing, with another route determination device which determines the route going through another node device among the plurality of node devices, the route information of the route determined by the route determining processing.