PURPOSE: To easily set tension with respect to an endless belt such as a timing belt, in a driving device transmitting driving force by using the endless belt, etc.

CONSTITUTION: A tensile force imparting device 1 is constituted so that the endless belt 2 such as the timing belt is wound on a sproket 5, and it is supported by a bracket 10. In this device 1, the bracket 10 is fixed on a supporting frame 12, by using a screw 12, via an oblong hole 11 provided on the bracket 10. At this time, the spring 16 is fixed in a state where the tensile force to the endless belt 2 is imparted by a spring 16. The spring 16 is left as it is, even after the tensile force is set, and can be used for adjusting the tensile force, as well, at the time of maintaining, etc.