To obtain a palatable and safe container made of styrenic resin foamed sheet having a mouth part high in strength and production thereof by applying bending curl processing to an opening flange by using a conventional curl device.

A styrenic resin foamed sheet is thermally molded to form a container main body 11 and the opening lid 14 having the part expanding in parallel to the bottom surface of the container main body provided to the outer periphery of the opening part of the container main body and the opening flange is subjected to curl treatment to form a container having a mouth part 23 formed thereto. In this container, the annular member 24 having the mouth outer peripheral shape of the container main body is involved when the opening flange is subjected to curl processing to form the mouth part.