A seal mechanism (10) can reduce noise during operation. The seal mechanism (10) is used for a fluid machine (P) to prevent a fluid from leaking out of a high-pressure space (H) into a low-pressure space (L) in the fluid machine (P). The seal mechanism (10) has an annular seal member (12) movable in a radial direction and a housing (11) disposed between a body (23) of the fluid machine (P) and a rotatable member (22) located inside the body (23) of the fluid machine (P) so as to receive the annular seal member (12). The annular seal member (12) has a first surface (12a) on a side of the low-pressure space (L) in the fluid machine (P). The housing (11) has a second surface (11c) facing the first surface (12a) of the annular seal member (12). The seal mechanism (10) has one or more passages (15) formed in the first surface (12a) and/or the second surface (11c).