Disclosed is a sound-absorbing silencer having a diffuse reflection structure. The silencer includes a housing including an inlet and an outlet formed in respective ends thereof to allow noise to be introduced thereinto and discharged therefrom and a noise-attenuating unit disposed in the housing to attenuate noise through diffuse reflection and absorption of the noise. The noise-attenuating unit includes a first diffuse reflection pipe disposed in the housing while being spaced apart from the housing, at least one second diffuse reflection pipe accommodated in the first diffuse reflection pipe while being spaced apart from the first diffuse reflection pipe to form a noise-attenuating path therebetween so that noise is diffusely reflected and absorbed while flowing through the noise-attenuating path, and a sound-absorbing member disposed between the first diffuse reflection pipe and the housing and in the second diffuse reflection pipe to absorb noise diffusely reflected in the noise-attenuating path.