To provide a molded article having a shape suitable particularly for surely molding a thin flat plate or a box type container free from warpage, deformation or uneven thickness in the molded articles capable of being used for thin plastic product such as a thin flat film sheet or various housing containers.

The thin flat plate like plastic made thin molded article is composed of (a) the thin flat plate 1 and a guide bar 6 provided on the thin flat plate 1 and having a shape in which bar-type ribs having wide or large diameters extend radially from the center of the molded article and the tips of the bar-type ribs having wide or large diameters have a shape that allows the molten resin injected from a gate into a cast to be accumulated temporarily before it flows into the thin plate, thereby providing a configuration in which the tips of the ribs do not reach the outer edge of the molded article.