Abstract: A testing apparatus for involute and helical gear teeth comprises a rotatable chucking device for the test piece, and a feeler device containing a feeler which can be moved along the tooth flanks of the test piece. A respective drive serves for driving the chucking device and the feeler device. A regulation device is provided for at least one of these drives, and a mechanical transmission arrangement is provided between the chucking device and the feeler device. A displacement pickup or transducer is arranged between two elements of the transmission arrangement and serves to measure the relative movement of both such transmission elements. An electrical circuit serves to infeed the measuring signals of the displacement pickup or transducer to the regulation device and such signals are superimposed upon the measuring signals of the feeler device.