The present disclosure relates to a drilling device for machining tubes in tube sheets of heat exchangers in a radioactive environment. A retaining plate is clampable in the tubes with at least two retaining fingers on a first side and a first drive, which drives a tool shaft, is arranged on a second side. A tool chuck on a first end side of the tool shaft is connected detachably to the latter, wherein a forward feed of the tool shaft is brought about by a feed device. In addition, the tool chuck is unlockable from the tool shaft by way of an unlocking instrument and the unlocking instrument is controllable by a remote-control device.