An operation determination processing section of a center extracts words included in the utterance of a driver and an operator, reads an attribute associated with each word from a synonym and related word in which an attribute is stored so as to be associated with each word, reads a domain of a candidate or the like for the task associated with the attribute from the synonym and related word in which domains of a candidate for a task associated with the read attribute or domains of a task to be actually performed are stored, totals the domains read for each word for words included in the utterance of the driver or the like, and estimates those related to a domain with a highest total score as the candidate for the task and the task to be actually performed. In this manner, it is possible to estimate the task with high accuracy.