A USB flash memory device connected to a USB bus includes a flash memory module including at least one flash memory, a USB connector for transferring data packets onto the USB bus and receiving the data packets from the USB bus, a USB controller for controlling the USB connector according to the data packets and for controlling storage of data in and retrieval of data from the flash memory module, a display controller for storing memory storage capacity information of the flash memory module in a usage display register, a display window for displaying a value that is based on the content of the usage display register, and a power unit for supplying a power to the USB flash memory device. The USB connector is configured to be coupled to the USB bus. The USB flash memory device further includes a folding portion which is proximal to the USB connector and enables the USB flash memory device to be folded. According to the present invention, data storage information of the USB flash memory device and additional information such as current time and data storage time can be visually determined through the display window, even in cases where the USB flash memory device is not coupled to the host platform. Further, the folding portion of the USB flash memory device enhances space usability and efficiency.