Abstract: A vehicle mounted type fuel testing apparatus comprises a fuel chamber; a first fuel pump for supplying fuel in the fuel chamber to a sample holding container and an auxiliary fuel tank; an analyzing device for analyzing constituents of the fuel accommodated in the fuel chamber; the auxiliary fuel tank for storing the fuel when it is determined that the fuel is normal fuel; the sample holding container for keeping the fuel when it is determined that the fuel is not normal fuel; a second fuel pump for supplying the fuel in the auxiliary fuel tank to a main fuel tank when the fuel is normal fuel; a third fuel pump for supplying the fuel in the auxiliary fuel tank to the outside when the fuel is not normal fuel; and a controller for controlling the above component parts.