A device for protecting a file system in an auxiliary storage device having a host interface configured to communicate with a host computer and a data storage device configured to store data, the device comprising: a user input device configured to receive information for selecting an operation mode of the auxiliary storage device and related information from a user, wherein the operation mode comprises a normal mode in which a protection operation is performed in a case where an access target is a file system object to be protected when the host computer accesses the auxiliary storage device, and a management mode in which a user designates a file system object to be protected as an object to be protected and set a protection type therefor; an object database to be protected in which the object to be protected designated by the user and the protection type set by the user are stored in the management mode, and a control device comprising: an operation control module configured to control the operation mode of the auxiliary storage device; an object database to be protected management module configured to store and manage the object to be protected designated by the user and the protection type set by the user in case that the operation mode is the management mode; a file system protection module configured to perform a protection operation for the object to be protected based on the protection type stored in the object database to be protected, when access of the host computer in the normal mode is target to the object to be protected stored in the object database to be protected in case that the operation mode is the normal mode. a user input device configured to receive information for selecting an operation mode of the auxiliary storage device and related information from a user, wherein the operation mode comprises a normal mode in which a protection operation is performed in a case where an access target is a file system object to be protected when the host computer accesses the auxiliary storage device, and a management mode in which a user designates a file system object to be protected as an object to be protected and set a protection type therefor; an object database to be protected in which the object to be protected designated by the user and the protection type set by the user are stored in the management mode, and a control device comprising: an operation control module configured to control the operation mode of the auxiliary storage device; an object database to be protected management module configured to store and manage the object to be protected designated by the user and the protection type set by the user in case that the operation mode is the management mode; a file system protection module configured to perform a protection operation for the object to be protected based on the protection type stored in the object database to be protected, when access of the host computer in the normal mode is target to the object to be protected stored in the object database to be protected in case that the operation mode is the normal mode. an operation control module configured to control the operation mode of the auxiliary storage device; an object database to be protected management module configured to store and manage the object to be protected designated by the user and the protection type set by the user in case that the operation mode is the management mode; a file system protection module configured to perform a protection operation for the object to be protected based on the protection type stored in the object database to be protected, when access of the host computer in the normal mode is target to the object to be protected stored in the object database to be protected in case that the operation mode is the normal mode.