The Clean Stocker is an AS/RS for temporary storage of work-in-progress products in the semiconductor manufacturing process and for conveying and storage of flat panel display (FPD) cassettes. The shelf modules are expandable to match the required numbers of semiconductors to be stored, and various stockers corresponding to the cassette size for each generation of FPD are available. Consideration is also given to high transfer capacity, prevention of dust generation, maintainability, and safety.