A vehicle diagnosing apparatus, a vehicle diagnosing system, and a diagnosing method enable the determination of completion of a repair or part replacement on a vehicle while adapting to changes in environment and overcoming temporal or spatial restrictions. The vehicle diagnosing apparatus reads diagnostic information from an on-board diagnosing unit on the vehicle that detects an abnormality in an on-board device. A result of a maintenance work performed on the on-board device is finalized by a maintenance result finalizing unit. A determination unit determines the appropriateness of the finalized maintenance work result with reference to determination information stored in a database that is continuously updated. The result of the determination is indicated by a notifying unit. Analogy is used to obtain the diagnostic information when the on-board device requires a long time or a certain condition to provide accurate diagnostic information.