A belt tensioning device for a crusher or a screening machine for tensioning at least one circulating drive belt which is deflected about a belt pulley of a drive and has a load strand and an empty strand. The drive can be driven with a crushing assembly, a screening unit, a generator, or the like of the crusher by the drive belt. The vibrational stress acting on the machine chassis can be significantly reduced in that the belt tensioning device has two tensioning rollers each of which is rotatably mounted on a holder of a tensioning part. One tensioning roller is paired with the empty strand and the other is paired with the load strand. Additionally, the two tensioning parts can be adjusted relative to each other between an open position and a tensioning position, in which the tensioning parts are held against each other at least opposite the tensioning direction. In particular the tensioning parts can be blocked against each other, and the complete closed system can be freely moved linearly using adjustment guides according to the load situation.