In a portable data erasing device, to prevent data leaks from magnetic disk devices to be disposed, data is erased by a simple operation. The data erasing device using a magnetic field generated by permanent magnets to erase data comprises a sliding tray, a main body and a swinging tray. The sliding tray is movable into and out from the main body, two permanent magnets, adjacently arranged so that the north and south poles thereof have mutually attracting polarities, are attached to the front end of the sliding tray. One end of the swinging tray is fixed to the upper surface of the main body by a shaft, so that a magnetic disk device can be mounted and swung on top of the main body. While the sliding tray is extracted stepwise from the main body, the magnetic disk device can be swung, and data on the magnetic disks erased.