A soundproof system includes a tube structure having one or more opening ends and a soundproof structure having an opening portion or a radiation surface. The following Expression (1) is satisfied in a case in which a phase difference between sound incident on the soundproof structure and sound re-radiated from the soundproof structure is defined a phase difference as θ1; for one or more maximum values of the pressure of sound formed in the tube structure, a distance between the opening portion or the radiation surface and a position where the sound pressure has a maximum value in the tube structure is L; a wavelength of the incident sound is λ; and a phase difference θ2 is defined as 2π×2L/λ: |θ1−θ2|≤π/2  (1). The soundproof system with a small size can obtain high transmission loss in a wide band.