PURPOSE: To prevent a drop in fan efficiency in terms of an in-air duct fan system where an axial fan is laid out under an air duct crossing state at a slanting posture, allowing its rotary shaft core to be slanted to an air duct axial core of a lower side air duct.

CONSTITUTION: There is installed an outlet air guide body 19 which provides a slanting guide plane m1 which extends to an air duct downstream side along the direction of a rotary shaft core P from an air duct wall near an end edge e2 located on the downstream side of the air duct out of both end edges e1 and e2 in the slanting direction and a subsequent guide plane m2 which extends to the downstream side along the direction of an air duct axial core Q of a downstream side air duct 6, communicating with the end edge on the downstream side.