An axial flow fan device 1 includes a first axial flow fan 10 and a second axial flow fan 20. The first axial flow fan 10 of a first casing 14 includes first engagement portions 152. Two sets of first engagement portions 152 are provided at positions which protrude outward in the direction of the axis x from a first base portion 16, and which are symmetrical with respect to the axis x, each first engagement portion 152 having a stepped portion in the radial direction. The second axial flow fan 20 of a second casing 24 includes second engagement portions 252. Two sets of second engagement portions 252 are provided on a second peripheral wall 241 at positions which are symmetrical with respect to the axis x, each second engagement portion 252 having a stepped portion in the radial direction.