PURPOSE: To miniaturize a medium supporting means by supporting a storage medium on its longitudinal sides and making a contact part between the medium and the supporting means shorter than the longitudinal side.

CONSTITUTION: Middle sections of parts of a guide plate 12 to be engaged with both side edges of an MD 1 are taken off, and instead of them, rollers 10 and 11 are fitted so as to press the edges of the MD 1. Thus, contact positions between the rollers 10 and 11 and the MD 1 are specified. Only one roller is constituted to be driven, and is preferably formed out of rubber on the driving side. The other roller is also preferably to be an elastic body, but may be formed out of plastics. The edges of the MD are pressed and supported by the rollers 10 and 11, and when the rollers 10 and 11 are rotated, the MD 1 is inserted/ejected.