A printing machine comprising a plurality of printing units (3) arranged in line one behind the other and an endless transport belt (4) for substrates to be printed, said transport belt running around, at least, two spaced-apart rollers (5, 6) and past said printing units. At least, two rollers (5, 6) are mounted on a coherent belt-carrying unit (9) from which, when being in a slack condition, said transport belt (4) may be stripped off. Furthermore, the printing machine features a drawer (24) which may be pulled out laterally and which is provided below said belt-carrying unit (9) as well as a holding device (11, 12, 13, 15, 16) holding said belt-carrying unit (9) and being switchable between, at least, two different conditions, in a first condition said holding device holding said belt-carrying unit in an operating position, and in a second condition said belt-carrying unit (9) resting loosely on said drawer (24). This permits a simple and quick belt changing.