To enhance the reliability of customer on maintenance job by adding adjustment reference being a more rational vehicle travel working rate based on the reference of a maintenance cycle.

The consumption parts such as tire and oil, and the service of vehicle washing and coating are set/registered with the number of standard secular limit months and a standard travel limit km as reference data for every vehicle. When the number of the standard time limit months of reference data is not registered, a period (number of months) calculated by dividing standard travel km, which is previously registered, by a vehicle travel working rate (average travel km) obtained by dividing the difference of the numbers of previous and this travel km by the period difference (number of months) of preceding and this entering dates of the customer vehicle is set and registered as the number of the standard limit months of reference data and it is predicted/managed. When the number of the standard time limit months and standard limit travel km are not registered, the period is set to be similar to the next suitable execution prediction period of the representative item of a service item group in the same group as the execution item.