A plastic sheet supplying apparatus for a thermoforming machine having an adjustable pin is proposed. Such a plastic sheet supplying apparatus for a thermoforming machine having an adjustable pin according to the present invention has the technical feature in which in a process in which a plastic sheet adhering to a material of a door trim is heated, fixing pins supporting a lower portion of an edge portion of the plastic sheet are configured to have adjustable positions so as to be moved in response to the change of the size of the plastic sheet caused by heating, so that the entire portion of the plastic sheet is uniformly heated and is also uniformly stretched without wrinkling, whereby the quality of a molded product is improved, and fabric consumption is reduced.