PURPOSE: To make uniform the light distribution by employing a short arc lamp as the light source and performing the exposure while rotating said lamp.

CONSTITUTION: A short arc lamp 11 is arranged such that its axis will be approximately perpendicular with the central axis Z of a glass panel 3, then the exposure is performed while rotating the short arc lamp 11 around the central axis Z. Consequently the exposure can be performed with high luminous intensity to shorten the exposing time and to make uniform the light distribution.