Apparatus for cleaning the descending branch of an endless transparent belt for rapid UV catalysis of the paint that coats panels made of wood or another material or other products with a flat surface, characterised by the sequence, from top to bottom, of at least the following means: - a first upper reverse roller that involves the descending transparent belt for the entire transverse extension thereof and a first bar for dispensing into the upper inlet formed by this reverse roller and by the transparent belt an amount of solvent useful for diluting the paint to be removed, this first reverse roller having features such as to distribute the solvent evenly on the belt and to perform thereon a first rubbing action also useful to detach the paint, to spread it and to make it more easily and rapidly reactive to the solvent and to distribute this diluted paint over a wide extension of the transparent belt; - at least a first doctor blade that involves the transparent belt for the entire transverse extension thereof and that forms with the upper section of this transparent belt an obtuse angle, all so that with the combined action of scraping and gravity this doctor blade collects and removes all the solvent and diluted paint coming from said first upper reverse roller; - a second upper reverse roller that involves the transparent belt for the entire transverse extension thereof, to subject it to a substantial cleaning action; - wherein at least said second upper reverse roller or both said reverse rollers (10,10') are formed by cylindrical metal rollers covered with several windings of a cloth, for example a felted cloth. - a bar combined with the second reverse roller for dispensing further solvent into the upper inlet formed by this reverse roller and by the transparent belt, all to perform a second mechanical operation of rubbing and of cleaning the transparent belt and of diluting any residual fluid paint, there being provided after these means, - at least a second doctor blade that touches the belt for the entire transverse extension thereof and that forms an obtuse angle with the upper section of this transparent belt, to collect and remove all the solvent and any traces of greatly diluted paint easily and totally and to then perform a drying operation of this transparent belt. - a first upper reverse roller that involves the descending transparent belt for the entire transverse extension thereof and a first bar for dispensing into the upper inlet formed by this reverse roller and by the transparent belt an amount of solvent useful for diluting the paint to be removed, this first reverse roller having features such as to distribute the solvent evenly on the belt and to perform thereon a first rubbing action also useful to detach the paint, to spread it and to make it more easily and rapidly reactive to the solvent and to distribute this diluted paint over a wide extension of the transparent belt; - at least a first doctor blade that involves the transparent belt for the entire transverse extension thereof and that forms with the upper section of this transparent belt an obtuse angle, all so that with the combined action of scraping and gravity this doctor blade collects and removes all the solvent and diluted paint coming from said first upper reverse roller; - a second upper reverse roller that involves the transparent belt for the entire transverse extension thereof, to subject it to a substantial cleaning action; - wherein at least said second upper reverse roller or both said reverse rollers (10,10') are formed by cylindrical metal rollers covered with several windings of a cloth, for example a felted cloth. - a bar combined with the second reverse roller for dispensing further solvent into the upper inlet formed by this reverse roller and by the transparent belt, all to perform a second mechanical operation of rubbing and of cleaning the transparent belt and of diluting any residual fluid paint, there being provided after these means, - at least a second doctor blade that touches the belt for the entire transverse extension thereof and that forms an obtuse angle with the upper section of this transparent belt, to collect and remove all the solvent and any traces of greatly diluted paint easily and totally and to then perform a drying operation of this transparent belt.