The present invention provides an automatic lubricant dispensing device, which comprises the following elements. A bracket is provided. A lubricant supplying device is mounted on a first end of the bracket. A dispensing gear is disposed on a second end of the bracket. A guiding arrangement is moveably mounted on the bracket, and including a pair of guiding rollers arranged coplanarly. Wherein a space is defined between the dispensing gear and the pair of guiding rollers in which a rack to be lubricated can fit therein, and the dispensing gear is adapted to mesh with the rack to be lubricated. Wherein the lubricant supplying device evenly dispenses the lubricant over the teeth of the rack by the dispensing gear which is completely and thoroughly meshed with the rack and transferred with lubricant from the lubricant supplying device. It is convenient, no need of labors and saving a lot of time. In addition, the lubricant can be evenly distributed to all the surface of the rack. In addition, the provision of the automatic dispensing device largely reduce the difficulty and time in lubricating the rack with dust free lubricant. A great deal of manpower and time has been saved. The environmental quality of the clean room has also been upgraded.