A synchronous movement device applied to dual-shaft system includes a first shaft and a second shaft, which are assembled with each other and synchronously rotatable. The synchronous movement device further includes a driver and a driving rail disposed on the first shaft, a reactor and a reacting rail disposed on the second shaft and a link unit connected between the driver and the reactor. When the first shaft drives the driver to rotate, the driver pushes the link unit to move along the first and second shafts to forcedly push the reactor to rotate in a direction reverse to the moving direction of the driver. Accordingly, the first and second shafts are synchronously rotated.