Abstract: A centrifugal compressor includes a compressor housing accommodating an impeller, and a casing treatment. The compressor housing include an air introduction hole through which air is introduced toward the impeller, an annular portion disposed inside the air introduction hole, and spoke portions. Each of the spoke portions connects an inner circumferential wall surface of the air introduction hole and the annular portion. The casing treatment includes a tubular portion provided on an upstream side of the annular portion in the air introduction hole in an introduction direction of the air, and wing-like portions. Each of the wing-like portions extends from the tubular portion toward a downstream side in the introduction direction of the air.

Abstract: An intake manifold (1) having a plurality of branch pipes (11) that link intake ports of an internal combustion engine and a surge tank (2) has rib portions (4) that extend from a surge tank surface (2a) to the branch pipes (11) and that link the surge tank surface (2a) and the branch pipes (11). In the surge tank (2), at least a portion of the surge tank surface (2a) that intersects with a center line of each branch pipe (11) faces an outer peripheral surface of each branch pipe (11). The rib portions (4) include at least parallel portions (4a) that extend substantially parallel with a center line of each branch pipe (11).