An inline axial flow fan includes a first fan including a first impeller, a first motor portion, and a first case, and a second fan including a second impeller, a second motor portion, and a second case, the first fan and the second fan being positioned in sequence from one axial side to another axial side. The first case and the second case are accommodated in a housing, and only one of the first case and the second case includes multiple slits that connect the inside and the outside of the first case and the second case in the radial direction.