PURPOSE: To supply the same light energy to an end and a center part of a form and secure sufficient fixation over the entire surface of a form by folding an end part of the reflecting mirror of a xenon lamp toward the end part of a form.

CONSTITUTION: The end part of the reflecting mirro 14 of the xenon lamp 13 is folded toward the end part 10a of the form 10 to form a folded part 14a. Therefore, the light from the xenon lamp 13 is reflected effectively by the folded part 14a toward the end part 10a of the form 10. Consequently, the quantity of light to the form end part 10a is nearly equalized to that of the center part 10b, and the light is utilized effectively to obtain sufficient fixation over the entire surface of the form.