Abstract: An apparatus for checking the alignment of laser beams for indicating a position in relation to a diagnostic and/or therapeutic machine, which has a isocentre, wherein the machine has a patient support movable in its position, laser beams and isocentre being aligned in relation to each other such that the laser beams intersect with each other in the isocentre of the machine, wherein the machine has the following a carrier element, which is provided with means for being arranged in a predetermined position on the patient support of the machine, a first and a second measuring device, each one at a time being equipped with connection means for the carrier element, wherein the first measuring device measures the position of the impingent laser beams with respect to a predetermined position in relation to the patient support, the second measuring device records the position of the isocentre in relation to the predetermined position of the first measuring device.