A driving device and chassis for a disk tray of an optical disk drive is disclosed. The tray of the optical disk drive is connected to the chassis. The front end of the chassis is provided with a driving means. By the driving of the driving means, the disk tray may open or close. A driven wheel serves to drive a decelerating gear set. The driven wheel has a hole that receives a rotary shaft retainer with a thread portion that screws into a boss on the chassis. An upper half of said rotary shaft screw is an axial portion, that extends through the hole in the driven wheel. Alternatively, a rotary shaft retainer may integrally formed with the chassis through a rotary shaft. The chassis is made of a general material. The manufacturing process is easy and the cost of the chassis of an optical disk drive is reduced.