The invention relates to a gear selecting device used for a motor vehicle having an internal combustion engine and a multi-gear transmission. The gear selecting device is equipped with first measuring devices (1, 2) used for detecting a numerical value of the speed (v) of the motor vehicle; a second measuring device (6) used for detecting a power demand (P); and calculation devices (3, 4, 5, 7, 8, 10, 11, 12) used for calculating required fuel consumption (k) used for satisfying power demands (P) of different gears of the multi-gear transmission under the condition of the detected speed (v) and used for outputting a gear (j, j-1) selected according to the calculated fuel consumption (k).