A microtome has a specimen holder which executes a vertical up and down movement relative to a cutting knife and which has a guide mechanism in which a sleeve is arranged so as to be horizontally displaceable. The sleeve is provided at its front end with a specimen clamping mechanism and in its interior with a micrometer nut which is secured against axial displacement and through which extends a micrometer spindle mounted on the guide mechanism. The micrometer nut has on its outer face a toothed ring which is connected operatively to a pinion connected to an electric motor. When the electric motor is activated the sleeve is displaced in the guide mechanism. The micrometer spindle extends, on the side opposite the specimen clamping mechanism, through the guide mechanism as a stub end on which is located a mechanical cutting-thickness advance mechanism. This advances the sleeve together with the specimen clamping mechansim, by a cutting-thickness set from outside the microtome, always in an uppermost position of the specimen holder.