A server device includes a tray having a lug, a hard disk unit removably disposed on the tray, and a handle pivotally connected to two opposite sides of the hard disk unit. The lug is formed with a slot thereon to define two inner edges opposite to each other. The handle is provided with a protrusion arranged in the slot. When the handle is rotated towards one end of the hard disk unit, the protrusion is rotated along with the handle to contact and push one of the inner edges of the lug, such that the hard disk unit is restrained by the tray after the hard disk unit is slid in relative to the tray.