PURPOSE: To obtain an integrally molded article without using adhesive agent that arouses trouble in environmental pollution and safety hygine by a method wherein semi-molded bodies different in shape that are molded separately are made to face each other and are stored in molds.

CONSTITUTION: A semi-molded body 1 in the shape of an inverse deep bowl having a flange-shaped mating portion 3 all over the periphery of a bottom end and a semi-molded body 4 in the shape of a shallow bowl having a flange-shaped mating portion 6 all over the periphery of a top end are stored and put on each other between a top force 12 and a bottom force 11 facing the mating portions 3, 6 to their respective concave portions 14, 13. When molten synthetic resin A is injected from an inlet 15, each cavity 13, 14 is charged with synthetic resin to integrate completely the mating portions 3, 6.