PURPOSE: To make highly accurate exposure attainable, by installing an actinometer, while automatically controlling time for the exposure so as to keep the quantity of light constant even if illumination reaching a panel surface is varied.

CONSTITUTION: A light receiver element 31 is disposed at a position capable of making light receivable after the light emitted out of a light source passes through a compensating lens 4 and a filter 5 while the light reaching a panel 11 is measured and calculated by an actinometer 32. The exposure value of the actinometer 32 is set in advance, and exposure action is performed by the way of opening a shutter 3 as calculating and integrating the illumination till reaching the setting value. The light receiver element has a built-in filter to pass through only the wavelength of light participating in the exposure of light of a sensitive suspension, so that exposure accuracy can be much improved by far.