To provide a method for manufacturing a plastic base capable of manufacturing the plastic base which can stably keep water repellency of the inner wall of a hole and the surface for a long time.

A bathtub part 20a is formed on a work holding stage 20 of an excimer laser processing apparatus, and its bottom face is coated with a laser reflecting layer 20b. After this bathtub part 20a is filled with a fluoro-compound solution S, a plastic base 100 being a work is placed on the work supporting part 20c immersed in the solution S, and the fluoro-compound solution S is placed between the laser reflecting layer 20b and the underside of the base. Then, the fluoro-compound solution S is frozen by a freezing chuck means, and the plastic base 100 frozen and fixed on the work holding stage 20 is irradiated with an excimer laser from its top face side to perform a hole processing.