An adjustment device (100) is used for the radial adjustment of the tools (15) in a peeling machine (10) for bars, tubes or similar oblong products to be worked (18), comprising feed means (17) to make each product to be worked (18) advance axially along a longitudinal axis (X) thereof, and a rotary head (12), which is provided with a central through cavity (13), in which the product to be worked(18) is able to run, and is able to rotate with respect to a fixed support (11), coaxially with said longitudinal axis (X), commanded by first motor means (Ml), and in which the tools (15) are mounted on the rotary head (12) and associated with corresponding adjustment units (16). The adjustment device (100) comprises second motor means (M2), able to drive the adjustment units (16), and a kinematic-differential unit (101) interposed between the second motor means (M2) and the adjustment units (16) and control means (50) associated at least with the second motor means (M2), so as to cause the selective and simultaneous activation of the adjustment units (16) and to effect the micrometric adjustment of the radial position of the tools (15) with respect to the longitudinal axis (X), also while the rotary head (12) is rotating.