A tray locking device of an optical disc drive adapted to lock and release a tray is provided. The optical disc drive has an optical head engaged with a lead screw and driven to move by the lead screw. The tray locking device includes a pushing member disposed on the optical head, a latching hook for latching and releasing a pin, and a transmission assembly disposed between the pushing member and the latching hook. The transmission assembly includes first and second lever elements. The first lever element pivoted in the tray has a slide slot having a first protrusion portion therein. The second lever element has a second protrusion portion adapted to move within the slide slot. When the tray is to be ejected, the lead screw drives the pushing member to push the second lever element, such that the second protrusion portion is aligned with the first protrusion portion.