PROBLEM TO BE SOLVED: To find a cause of a failure at a working site without a service enginner taking a computer to the working site as well as to centralizedly control an overall parking area.
SOLUTION: When abnormality occurs in a parking area, a data of a sensor, or the like at the time of a failure is transmitted to a host computer on the central side through a public line in a system to diagnose a large number of the failures of the parking area. Thereafter, in accordance with the data, a cause of the failure is assumed from the data of the sensor, or the like and question items and the cause of the failure are transmitted to the parking area where the failure occurs at a host computer 40.