To obtain an external type optical disk device which is manufactured at low cost, has high shielding effect against an electromagnetic wave, and never spoils the smoothness of movement of an optical head.

A mechanism unit 4 has the optical head 21 and is covered with a box-shaped shield lid member 13 made of a tin plate and provided in a housing 2 as a synthetic-resin molded component. Above a sub-guide rail 25 of the optical head 21, a permanent magnet piece 27 is provided which magnetically attracts the sub-guide rail 25 to prevent the optical head 21 from having play in moving. A thin and long opening window 45 is formed in a part of a ceiling plate part 40 of the shield lid member 13 which faces a range wherein the permanent magnet piece 27 moves.