A separating device includes a separating unit and a crack front line adjusting unit. The separating unit is adapted to separate the flexible film and the substrate. During the process of separating the flexible film from the substrate, a crack front line is formed between a portion of the flexible film not separated from the substrate and a portion of the flexible film separated from the substrate. The crack front line adjusting unit is adapted to sense a relative displacement state of the flexible film and the substrate for determining a distribution of the crack front line, and is adapted to apply a down pressing force to the flexible film or the substrate and increase or decrease the down pressing force according to the relative displacement state, so as to adjust the distribution of the crack front line.