A partition wall sound insulation structure includes: a floor material on which a floor surface facing an indoor space side is formed; a ceiling material on which a ceiling surface is formed, the ceiling surface being opposed to the floor surface in a vertical direction with an indoor space interposed therebetween; a partition wall that extends in the vertical direction so as to partition the indoor space in a horizontal direction and that is disposed with a gap from at least one surface of the floor surface and the ceiling surface; and a sound insulation material made from an elastic material and including a portion disposed in the gap while being compressed in the vertical direction.