Abstract: In a device for measuring the radial blade clearance between the moving-blade tips (6) and the blade carrier (4) of thermal turbomachines with the use of a measuring needle (7) which is guided along in an opening (16) in the blade carrier (4), is accommodated by the blade carrier (4) in a seat (8), projects radially opposite the moving-blade tips (6) into the flow duct (17) and can be abraded, the measuring needle (7), at its end remaining in the blade carrier (4), is fastened to a flexible guide part (10) projecting from the machine, the other end of the guide part (10) being connected to components (11), for example a screwed socket or a hydraulic cylinder. The components (11) permit a linear movement of the guide part (10), which is surrounded outside the outer casing (5) by a flexible tube (12), and between outer casing (5) and blade carrier (4) by a rigid guide tube (14). The device is especially suitable for measuring the transient blade clearance.