A navigation system has: a candidate input device 14 for inputting a search key; an input vocabulary storage 11 that stores words to become candidates of a search key input from the candidate input device; a vehicle information storage 12 for storing vehicle information relating to a vehicle; a preference information storage 13 for storing preference information representing user' preference in connection with the words stored in the input vocabulary storage; an input word estimating module 17 for searching the input vocabulary storage for words corresponding to the search key input from the candidate input device, and for estimating the words obtained by the search in accordance with an order of priority based on the vehicle information read out of the vehicle condition storage and the preference information read out of the preference information storage; and a candidate output device 15 for outputting the words delivered from the input word estimating module as candidates.