Six auxiliary sheet holders SH2 and SH3 temporarily holding a sheet S are minutely driven in the −Z-axis direction by a control device so that holding surfaces thereof are positioned on the slightly lower side (−Z side) of the holding surface of the sheet holder SH1. Accordingly, an appropriate tension is applied to the sheet S in the width direction (Y-axis direction) and the longitudinal direction, so that the center portion of the sheet S is fixed onto the holding surface of the sheet holder SH1. That is, in the state where an XY two-dimensional tension is applied to a separate area SAi of the sheet S, a rear surface portion corresponding to the separate area SAi of the sheet S is changed in accordance with the flat shape of the holding surface of the sheet holder SH1. In addition, in the state where the tension is applied to the predetermined area in the longitudinal direction and the width direction, the rear surface portion corresponding to the predetermined area of the sheet material S is changed in accordance with the flat reference surface so as to be flattened. In addition, the predetermined area of the flattened sheet material is irradiated with an energy beam so as to form a pattern thereon.