To provide an air passage type silencer that can suppress generation of a wind noise, that has a high sound attenuation effect in a low-frequency band, and that has high air passage performance. The air passage type silencer includes an inlet-side ventilation pipe, an expansion portion that communicates with the inlet-side ventilation pipe and of which a cross-sectional area is larger than a cross-sectional area of the inlet-side ventilation pipe, an outlet-side ventilation pipe that communicates with the expansion portion and of which a cross-sectional area is smaller than a cross-sectional area of the expansion portion, an opening portion structure of which a cross-sectional area gradually decreases from an inside of the expansion portion toward a connection portion between the expansion portion and the outlet-side ventilation pipe, a rear surface space that is surrounded by the opening portion structure, a side surface of the expansion portion that is on an outlet-side ventilation pipe side, and a peripheral surface of the expansion portion, and a porous sound absorbing material that is disposed at least in an opening portion of the rear surface space.