The invention relates to an apparatus for positioning a sample carrier plate, wherein the apparatus comprises a main body for receiving the sample carrier plate, positioning stops which are disposed in opposing first corner regions of the main body and are prestressed for clamping the sample carrier plate and mounted displaceably, an actuating device which is disposed at the main body and is equipped such that by actuating the actuating device the positioning stops can be transferred between an operating state engaging the sample carrier plate and an operating state releasing the sample carrier plate, and comprises a force transmitting element which is equipped to transmit an actuating force from the actuating device to the positioning stops.