The invention provides a disk device in which simplification of parts, and improvement of operability are performed with simple constitution, in especially traverse mechanism and gear part assembly structure. When a shift lever is fitted under a front part of a traverse mechanism, dampers have previously been fitted in a total of two, front-left and front-right, parts, called mount parts, of a mechanism chassis. A flat gear rotatably engages with a cylindrical sleeve protruding downward from the front-right mount part of the mechanism chassis. A feed gear in a rear part of transmission means rotatably engages with a boss protruding downward behind the sleeve, and is prevented from dropping off with a screw put from below. Now, the flat gear is, in a rear part thereof, supported by the feedgear, and is thereby prevented from dropping off.