PURPOSE: To shorten the time of a storage medium attaching/detaching processing by predicting the keeping position of a storage medium which is mounting-requested next based on the content of a storage medium mounting frequency storage means and positioning the storage medium storing pockets of a transportation mechanism in a prediction position.

CONSTITUTION: At least more than two storage medium storing pockets of the transportation mechanism 7 are provided, and the mounting frequency storage means 5 of the storage medium, which corresponds to the storage medium keeping position in the keeping mechanism 1, is provided. Then, the past mounting frequency for respective storage mediums is stored as hysteresis information and the keeping position of the storage medium whose probability to be mounting-requested next is high is predicted. The storage medium storing pockets of the transportation mechanism 7 is positioned in the prediction position. Thus, the time of the storage medium attaching/detaching processing can be shortened.