The degree of freedom of a sound-absorbing device in terms of size is increased, maintaining easy mounting operation of the sound-absorbing device, even if the sound-absorbing device has a greater length.The sound-absorbing device 1, which alleviates and absorbs a sound generated by fuel movement in a fuel tank in such a state that the sound-absorbing device is put into the tank through an opening E formed in the tank and is mounted to the tank, has a three-dimensional structure, which has a narrower width X than a width of the opening and a greater length Y than the width of the opening E; and the sound-absorbing device comprising plural sound-absorbing parts 2A and 2B coupled together through a coupling portion 3 in an intermediate position in a longitudinal direction extending along the length Y.