To provide a method and a device for deleting data of a storage device with excellent confidentiality by which only a piece of data on the storage device such as a hard disk drive is selectively deleted and it is impossible to restore the data by restoration software etc.

In the method for deleting data of the storage device in a computer, entity data and an operating system are deleted by overwriting data for deletion after performing format processing to the storage device 18 after recognizing the storage device 18 as an external storage device by a computer 1 for data deletion by connecting the storage device 18 in which the entity data which is an object to be deleted is stored to the computer 1 for data deletion.