A pneumatic tire has an inner shoulder, an outer shoulder and a tread therebetween. The device may be provided in the form of a kit. The controller further includes a response-delay-time computing portion for computing a response delay time of the pressure reducing valve based on a command timing and a fuel pressure variation timing. Each of signal generators is operable to generate an output signal based on at least the detection signal outputted from one of the photo detectors. The diesel particulate filter may be one of a plurality of honeycomb cells. The two frictional resistance producing members include a radial plate spring made of resilient metal which includes a ring portion and a plurality of radial projections which project radially outwards from the ring portion; and an annular friction member having a pressure surface which is brought to be pressed obliquely against flat surfaces of the plurality of radial projections.