PURPOSE: To obtain wide and reliable data for economical running, by changing sampling time in correspondence with input setting.

CONSTITUTION: Sampling time can be changed in correspondence with input setting by a central control circuit 6. A fuel consumption value is computed by an operating circuit 5 based on vehicle speed pulses P, which are inputted within the preset time, and the accumulated value of the corrected fuel injection amounts. A pattern is changed in proportion to the fuel consumption value. Thus the instantaneous fuel consumption and the average fuel consumption for a long time are arbitrarily displayed. The driver obtains the optimun pushing of an accelerator for economical running by observing the instantaneous fuel consumption or can grasp the optimum speed by observing the average fuel consumption for a long time.