To provide a sound insulation door manufacturing method which can efficiently manufacture the sound insulation door with a smaller number of steps than that in the conventional soundproof door manufacturing method.

A sound insulation door manufacturing method includes steps of: preparing two single-structured decorative plates (2, 3) beforehand and putting one decorative plate (2) on a working surface; preparing beforehand a core material (1) including an outer frame (10) and honeycomb-shaped paper core plates (101, 102) bonded to the inside of the outer frame (10) and having a plurality openings (103) on both front and rear sides, and applying an adhesive to the surfaces on both front and rear sides of the outer frame (10) of the core material (1) and the edges of the openings (103) on both front and rear sides of the paper core plates (101, 102); setting and mounting the adhesive-applied core material (1) on the top surface of the one decorative plate (2) on the working surface; setting and mounting the other decorative plate (3) on the mounted core material (1); and pressing the whole of a laminate consisting of the core material (1) and the decorative plates (2, 3) in the thickness direction to bond them.