PURPOSE: To improve the processing efficiency of a system by holding plural cassettes in a stack state, slanting their opening parts upward and downward and taking or storing panels out of or in the cassettes through a unlocking means, and taking an optional panel out freely.

CONSTITUTION: Plural cassettes 20 stored in a stack state by a rack material 21 and plate materials 21a and 21b have their cassette opening parts 24 slanted downward by a crank mechanism 40 and the whole is moved up or down to the position where a desired cassette and unlocking means 23a and 23b abut on each other. The front ends of the unlocking means are moved and put be tween panel holding members 32a and 32b in the cassette and then the clamped radiation image conversion panel P is unlocked and taken out of the cassette by its own weight, so that the panel is conveyed to a read part. A panel after use is stored by its own weight in a cassette whose opening part is slanted upward through unlocking means 23a' and 23b'. Thus, an optional panel is taken out freely and the processing efficiency of the whole system is improved.