A repairing method using a lance for repairing an oven wall surface of a coke oven comprises the steps of arranging a distance sensor at a top end of the lance, quantitatively measuring a depth of a worn or a damaged area by the distance sensor, and blowing a repairing material from a repairing nozzle to the worn area in accordance with a measurement result to thereby repair the worn area. The lance used in this repairing method has a multistage structure having a polygonal cross section and is extendable. With this structure, the oven wall surface can be scanned in a linear fashion or along a plane. If the top end of the lance is movable in accordance with a basic motion pattern and/or a travelling pattern, it is possible to readily repair a repair range having a complicated shape.