Abstract: An apparatus (10) for calibrating measuring instruments, such as bore gauges and the like, comprises means (12) for supporting the apparatus and calibrating means having contact means for the respective measuring ends (15, 17) of the instrument to be calibrated, these means being, for each measuring end of the instrument to be calibrated, in the form of a first and a second contact surface (31, 33d). The apparatus also comprises at least one adapter element (50) on at least one of the contact surfaces of the calibrating apparatus, this adapter element (50) being designed to receive and support a respective end of the measuring instrument by adjusting to its profile. The adapter element (50) comprises means which engage a respective end of the measuring instrument and which are made in such a way that they can receive different measuring instruments.