An expansion device configured for securely holding a rolled material when the rolled material is handled on roller is disclosed. The expansion device includes a roller spindle, two expansion members, a fixing sleeve, a clamping nut, and a locking member. The locking member moves toward the expansion members, so that the two expansion members expand toward the fixing sleeve, and protrusions which are formed on the expansion members are pressed outward through fixing holes of the fixing sleeve, and then resist against an inner surface of rolled material inside a rolling hole formed therethrough the rolled material. Thus, the rolled material is held securely by the expansion device.