An air cleaner including a front housing, a rear housing, and a filter. The filter includes a plurality of parallel folds and partitions a pre-filtering chamber and a post-filtering chamber. The air cleaner circulates air, which enters the pre-filtering chamber through an inlet port, to the post-filtering chamber to filter the air. The pre-filtering chamber includes a diffusion zone located outward from an end of the filter in a folding direction of the filter. The inlet port extends in a direction orthogonal to the folding direction of the filter along a plane parallel to the filtering surface of the filter and opens in the diffusion zone.