An endoscope with an instrument housing and with a shaft that is mounted on the distal end of the instrument housing and consists of an outer tube and an inner tube that is mounted at least partly in the outer tube, so that the outer tube and the inner tube are mounted on the instrument housing so that they can move with respect to one another in the axial direction of the shaft. To provide an endoscope that ensures a constantly fluid-tight relative motion of the two shaft tubes with respect to one another, it is proposed with the invention that the outer tube and inner tube should be mounted on the instrument housing so that they are mobile with respect to one another in the axial direction of the shaft by means of at least one flexible membrane.