Abstract: Thread grooves (internal threads) for electrical connection are directly formed in two mounting portions among a total of eight mounting portions provided in the side surfaces and bottom surface of the base plate of a magnetic disk device which are provided in two positions electrically far from the magnetic head with respect to the noise frequency. The two mounting portions are grounded to the chassis of a system having the magnetic disk device mounted thereon. Mounting members having the electrical insulating property are fitted in the mounting holes of the six mounting portions which are disposed in positions electrically closer to the magnetic head and the mounting members are electrically isolated from the chassis of the system when they are mounted on the chassis of the system by use of fixing screws.