A communication terminal apparatus included in a navigation system having a fixedly installed information server apparatus and communication terminal apparatuses mounted one by one on a plurality of movable bodies for communicating with the information server apparatus via a mobile communication network, the system changing the movable bodies performing navigation by switching a connection between each of the communication terminal apparatuses and the information server apparatus, wherein the communication terminal apparatus comprises a sending device for, on starting or stopping, sending to at least any one of the information server apparatus and the other communication terminal apparatus switching information for switching the connection to the information server apparatus to any one of the communication terminal apparatuses, and performs the navigation based on data on the navigation before switching the communication terminal apparatus in the case where the connection is switched to the communication terminal apparatus.