Spray unit with a rotatable nozzle as well as a blasting device A blasting device has a spray unit for spraying blasting agent onto the surface to be treated. The spray unit has an insert 23' in which a nozzle 13' is rotatable. This nozzle 13' is provided with a number of spray channels 19' which are at an angle 21' relative to the supply direction 17 of the blasting agent. The blasting agent is pressed through the spray channels 19' under pressure and exerts a force on the wall of the spray channels 19' causing the nozzle 13' to rotate. The jets emerging from the rotating nozzle 13' will make a rotating movement. The joint area of the cross-sections of the spray channels 19' is larger than one third of the cross-sectional area of the circular- cylindrical part of the nozzle. The angle 21' at which the spray channels are located with respect to the supply direction 17 of the blasting agent is greater than zero and less than 10 degrees.