A tray-like container of a plastic coated paper blank having a base panel, which has four or more even numbers of side edges, side walls, corner portions, a peripheral portion extending along side walls and corner portions, and a pig-tail like folding line formed in each corner portion of the peripheral portion, of which a flange of the tray-like container is formed. The pig-tail like folding line assists in the outward bending of the peripheral portion so that it forms the outwardly projecting flange of the tray-like container. The outer shape of the tray-like container is forcedly molded by a movable and stationary complementary moulds.