To provide the manufacturing method of a sound-insulating panel, by which a frame material can be bonded and fixed surely onto a panel board by press works in one process, and to produce the sound-insulating panel having high sound-insulating performance and stable quality by the manufacturing method.

In the manufacturing method of the sound-insulating panel, a gas is injected into a pressurizing tube 6 arranged among the frame materials 3 disposed onto one rear of a pair of mutually opposed panel boards 4, 5 and the rear of the other panel board opposed to the frame material to expand the tube 6 while the tube 6 is pressed from both surfaces of the panel boards 4, 5 and the frame materials 3 are bonded with the rears of the panel boards 4, 5 when the sound-insulating panel in which the outer circumferences of the panel boards are sealed and a sealed air layer is formed on the inside is assembled.