To provide a driving device which raises the accuracy of a length measuring meter by increasing the quantity of the amount of recovery of heat generated from a driving part, by reducing the increase in a design pressure resistance, by suppressing the increase in the pressure of a cooling medium route due to the increase in the supply quantity of a cooling medium, and by enabling the design pressure resistance due to the decrease in the pressure of a cooling medium route; and which achieved the increased output more than before.

The pressure of the cooling medium supply route entirety becoming a closed circuit which flows from a tank for storing the cooling medium to a heating element, and again returns to the tank for storing the cooling medium by reducing in the pressure in the tank for storing the cooling medium. Accordingly, the design pressure resistance is reduced.