PURPOSE: To uniformly and stably obtain a large quantity of colored plastic articles, especially, plastic lenses by forming a colored layer on a plastic base material by coating the base material with ink by an ink jet system.

CONSTITUTION: A colored layer is formed on a plastic base material by coating the base material with ink by an ink jet method. For example, a head of an ink jet system generating a volumetric change in ink by applying an electric signal to a piizoelectric element to fly ink particles is used. A plurality of nozzle heads each having a plurality of nozzle orifices arranged thereto in a row are arranged above lenses and the timing of the movement of the lens set on a moving stage and the ejection of ink is taken to apply an arbitrary hue or pattern to the lens.