A sheet material supply roll wrapped on a core tube including a reserve segment of sheet material spirally wrapped around the core tube with a supply segment of sheet material spirally wrapped on top of the reserve segment of sheet material. On the two lateral edges of the center part, a supporting part is pivotally connected in each case by way of a film hinge, which supporting parts can be swivelled toward lateral edges of the headrest. When the coverage restriction is not satisfied, an optimum black colorant quantity is calculated by adjusting the input black colorant quantity, and an optimum color signal satisfying the coverage restriction is calculated to generate an output color signal with the optimum black colorant quantity in the restriction black colorant quantity calculating section and subsequent processings. The front panel is formed on the front of the main chassis and has a spacer formed in an inside thereof.