PURPOSE: To execute ranking of a result of diagnosis, by comparing plural different reference values with a measured value with respect to each diagnostic item.

CONSTITUTION: When a measured value from a sensor is provided to a computer 4 connected to an input means 1 for inputting a car kind, an engine type, diagnostic contents, etc., and an input means 2 of a remote use input and display device, plural reference values read out of a reference value storage means 6 with respect to each diagnostic item are compared with the measured value. Subsequently, a result of diagnosis is ranked and decided, and the result of diagnosis is displayed and recorded in a display means 7 and a recording means 8 by separating it to each rank. In this regard, by combination of results of decision of diagnostic items of two kinds or more having casual relation, a part in which abnormality is generated actually can be discriminate exactly.