A packaging container which includes a synthetic resin container body having a flange part and the cover member heat-sealed to the flange part of the container body. The cover member includes (1) an upper member in which inner surfaces of resin films are positioned opposite to each other to form an abutted part, an unsealed part communicating with the inside of the container body is formed by heat-sealing a peripheral edge part of the abutted part excluding one side of the abutted part forming a base part, and the steam releasing seal part is formed at the abutted part and (2) a lower member which covers a lower surface of the upper member and in which a steam guide part communicating with the inside of the container body is formed at or near the base part of the abutted part.