Any anomaly in energy transfer is appropriately diagnosed in a vehicle. The energy transfer system of a vehicle is provided with: an input energy computation means (e.g., the chemical energy of fuel computation means) for determining the input energy of the energy transfer system; an output energy computation means (e.g., the vehicle kinetic energy computation means) for determining the energy output of the energy transfer system; and a comparing means (e.g., the comparing means) for comparing the input energy with the output energy. Any anomaly in the energy transfer system (e.g., any anomaly in fuel efficiency) is determined based on the result of comparison by the comparing means.