The invention refers to a fast steel knife replacement system in a cutter head, using two tools specially developed and adapted to act upon the cutter head cylindrical body and force the release of the knives. To the cutter head, built of steel with slots designed for insertion of gibbs and knives, are fixed at the extremities two discs (10) machined at half-thickness and equipped with pins in the inner sides, which allows the insertion of a lever tool (09) that forces the downward movement of the gibb and consequently the knife release. The operation ends with the magnet tool (01) placing or removing the knife. The latter was designed with a specific profile adapted to the lateral sides of the cutter head slot and the gibb, for plane and double cut and allows perfect fixing without the need of calibration.