An injection-molded case and a manufacturing method thereof having antenna patterns are formed in the injection-molded case by only one insert injection molding process, without a second insert injection molding process as required in the conventional manufacture. The injection-molded case preferably includes: one or more antenna patterns fabricated by a press process; and an injection-molded case part having the antenna patterns provided therewithin, which is fabricated by fixing the antenna patterns on an injection mold and carrying out only one insert injection molding process.