PURPOSE: To obtain the determining means of read condition which performs the preprocessing of a previously read histogram and removing a noise part from the previously read histogram, and then decides on proper read condition stably on the basis of a real accelerated phosphorescence quantity histogram or histogram nearly coincident with it with respect to a radiation image information recording and reproducing system used for medical diagnosis.

CONSTITUTION: A histogram part A between a maximum value S1 and a specific value is calculated from the previously read histogram, and the maximum and minimum quantities Smax and Smin of accelerated phosphorescence within the range (range of the quantity of accelerated phosphorescence) of desired image in formation are calculated from said histogram part A. A part D in a figure is a skin part and when information on this part is not necessary, the desired image information range corresponds to the remaining part E, so that the maximum and minimum quantities of accelerated phosphorescence of this part E are found as Smax and Smin.