Further, a bypass path 16 via which the inside of the air cleaner case 11 communicates with an external space S3 is formed in the air cleaner case 11. Hereby, the air in a motor room where the air cleaner 1 is placed can be introduced. The bypass path 16 communicates with an inlet-side space S (described later) on the side closer to the inlet 14 than the locking projection 17. Further, the bypass path 16 also communicates with the inlet-side space S1 on a side closer to the outlet 15 than the locking projection 17 via an opening 18 formed in the inlet-side case member 12. In fact, as illustrated in FIG. 1, the bypass path 16 is stuffed with a sealing member 6 (a rubber lip, a urethane sponge, and the like) so that the communication with the inlet-side space S1 on the side closer to the inlet 14 than the locking projection 17 is blocked. Accordingly, the bypass path 16 communicates with the inlet-side space S1 only via the opening 18.