To provide an automatic blade replacement device for a slitter by which simplification of replacing/adjusting work of a slitter blade or the like in off-line can be realized and an operation rate of a line can be improved.

A strip material is cut by rotating a pair of upper and lower arbors 2, 3, which are provided with an element composed of a plurality of the slitter blades and annular spacers, and arbor shafts, and supported freely rotatably in the slitter 1. The automatic blade replacement device for the slitter 1 has the following constitution. One adjusting part 4 supporting the arbors 2, 3 is erected to the direction orthogonal to the arbors 2, 3 freely slidably. Dummy arbor shafts DA1-4 are horizontally protruded to one side of the slitter 1. An oscillation stand 7, which oscillates the dummy arbor shafts DA1-4 and reciprocates them between the slitter 1 and an element rack 8, is arranged. The phase of the dummy arbor shafts DA1-4 is changed by a rotation mechanism 10 composed of a planetary gear mechanism. The dummy arbor shafts DA1-4 are connected to the arbor shafts. The element is transferred via pushers 17, 18.