Abstract: A lighttight envelope for housing a stimulable phosphor sheet therein is fabricated of a flexible light shielding material and has a size sufficient to house the stimulable phosphor sheet therein. The lighttight envelope comprises an upper sheet and a lower sheet closely contacted with each other at least at one side and open at least at one side opposite to the closely contacted side and at portions of two sides adjacent the ends of the opposite side up to such positions that access to a part of the stimulable phosphor sheet housed in the lighttight envelope is allowed, thereby forming a wide inlet for the stimulable phosphor sheet. A small face-to-face fastener is positioned at a part of the opposite side.