The invention relates to a drilling device and a drilling method for drilling inside a casing tube with a drilling apparatus, which has a supporting frame with a fastening means for fixation with respect to the casing tube and a drilling tool, which is driven in a rotating manner via a telescopic rod by means of a drill drive arranged on the supporting frame. At the upper end of the casing tube a receiving part is arranged in accordance with the invention, onto which the supporting frame can be fastened. The receiving part is adjustably supported between a drilling position and an offset position, in which the receiving part is laterally offset with respect to the casing tube.