Files disappeared

Hi Masayuki, 

Welcome to Box Community and glad to assist! 

Notes:

• When items are deleted from a collaboration folder, both the owner and the person who deleted the item can recover the items from the Trash. 
• If you are removed as a collaborator from a file or folder that you've deleted, you no longer see that item in Trash. To see the item in Trash, you must be again added as a collaborator to that item.

To restore specific items in Trash:

The steps below apply whether you’re selecting from search results or from all Trash items.

1. Hover to highlight the row of the item you want. The More Options ellipsis (…) displays.
2. Click the ellipsis (...).  Then: 

• To return the item to its original location in Box, click Restore.

3. At the prompt, click Okay.

Hope it helps!