Abstract: An adjusting device for adjustable rotor vanes of a machine rotor including a first gear wheel (34) on a machine shaft (2) and a second gear wheel (44) on an adjusting shaft (4), whereby a relative rotation between the machine shaft and the adjusting shaft can be initiated through a transmission (38) by either of two braking devices (12, 22). The adjusting device of the invention makes it possible to adjust the rotor vanes with a simple construction and with a good degree of efficiency while simultaneously providing good accessibility for assembly and service. A further brake (40, 41) is provided between the transmission (38) and the machine shaft (2) or the adjusting shaft (4) to maintain synchronous rotation of the adjusting shaft (4) with the machine shaft (2) during normal operation, i.e., so long as no adjustment of the rotor vanes (64) is to take place.