Air passage type silencer

An air passage type silencer comprising:

• 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;
• and
• an outlet-side ventilation pipe that communicates with the expansion portion and of which a cross-sectional area is smaller than the cross-sectional area of the expansion portion,
• wherein one opening edge surface of the inlet-side ventilation pipe and one side surface of the expansion portion are connected to each other, and one opening edge surface of the outlet-side ventilation pipe and another side surface of the expansion portion are connected to each other,
• a level difference d satisfies Equation (1):
• d≥100 μm,
• satisfies Equation (2):
• d≤25×Sa+193 μm in a case where an arithmetic average height Sa is equal to or smaller than 50 μm, and
• satisfies Equation (3):
• d≤1450 μm in a case where the arithmetic average height Sa exceeds 50 μm,
• where Sa (μm) is an arithmetic average height of a surface on a central side in the expansion portion and
• d (μm) is an average value of level differences between a ventilation pipe interior wall and the surface on the central side at at least one of a connection portion between the expansion portion and the inlet-side ventilation pipe or a connection portion between the expansion portion and the outlet-side ventilation pipe.