A CPU of a navigation apparatus stores public keys to which priorities are set and which are published by an information distribution center in a public key storage section. The CPU of the navigation apparatus extracts an electronic signature of distribution data which is distributed from the information distribution center and verifies the electronic signature by using only ‘valid’ public keys among the public keys in order of the priorities. The CPU of the navigation apparatus determines that the distribution data is valid information which is distributed from the information distribution center when the electronic signature passes verification.