The invention discloses an automatic loading device of a lathe applicable to disc-type parts. A sliding plate is arranged in the square-shaped hole of a rectangular frame in a penetrating manner; the left plate surface of the sliding plate is vertically provided with a dovetail groove which is in sliding fit with a dovetail guide rail on the right plate surface of a fixed plate; the top surface of the fixed plate and the bottom surface of the rectangular frame are fixed; the front side surface of the fixed plate is fixedly provided with a limited block; the right part of the limited block is vertically provided with stripy holes which are internally provided with limit screws in a penetrating manner; and the limit screws and the front side surface of the sliding plate are fixed simultaneously. The automatic loading device can be used for replacing workers to realize automatic loading, so that the labor intensity of the workers is greatly reduced, and the working efficiency is also greatly improved; and the loading device can be matched with a numerical control lathe so as to realize unattended production, and is simple in structure, smart in concept and suitable for large-scale promotion and application.