To prevent breakage of storage media and a mechanism inside a slot when contriving to have a slot in common for two types of storage media having mutually different sizes.

This storage medium loading mechanism is provided with a holder 39 for holding two types of storage media 100, 200 having different sizes in the direction of insertion into the slot 4, adapted to be moved in the state of holding one of the storage media between a discharge position and a first storage recovery position or a second storage recovery position having a short distance from the discharge position, energizing means 57 for energizing the holder to the first storage recovery position in the direction of insertion when the storage medium having a larger size in the direction of insertion is held by the holder, and locking means 51 for locking the holder to the second storage recovery position when the storage medium having a smaller size in the direction of insertion is held by the holder.