PURPOSE: To prevent dust and finger prints or the like sticking onto recording sheets so as to perform recording with no image disturbance, by enabling the recording sheet extracting port of a sealed cassette casing in which recording sheets are stored and which can be removably mounted on a recording apparatus, to be opened.

CONSTITUTION: Recording sheets 4 having been produced in such a condition that dust or the like is prevented from sticking thereonto and stored in a cassette casing 2 are delivered to the user with the casing being closed by a cover. In this phase, the casing is sealed so as to prevent dust or the like from entering thereinto during storage or shipping. It is therefore not necessary to touch the operator's finger directly to the recording sheets upon use, thereby there is no possibility of finger prints or the like sticking onto the recording sheets. Further, the recording sheets are not exposed to the outside even they are set in a recording apparatus, and it is therefore possible to prevent dust or the like from entering into the casing, thereby it is possible to carry out recording of image with no disturbance.