A navigation system includes a navigation apparatus, a data center, a communication-defective region acquisition device, a communication-defective region search device, and a target region specify device. The data center performs transmits an update data of a target region to the navigation apparatus. The communication-defective region acquisition device acquires information of a communication-defective region. The communication-defective region search device searches for a part of the communication-defective region as a target communication-defective region, which includes a route scheduled to go through. The target region specify device specifies the target region based on the target communication-defective region. The data center includes an update data transmission device that transmits the update data of the target region to the navigation apparatus before the navigation apparatus enters the target communication-defective region.