An object is to supply a sufficient amount of air to a fuel cell stack in a fuel cell vehicle when the fuel cell stack is mounted below a floor, the fuel cell stack configured to draw in air through an intake duct and discharge air to the exterior through an exhaust duct. An air introduction surface (26) faces upward or downward in a vehicle upper and lower direction, an intake passage portion (30) of the intake duct (28) extends along the air introduction surface (26) and vertical walls (31, 32) of left and right end portions of the fuel cell stack (11) while a pair of air introduction ports (33, 34) opens in left and right end portions of the intake passage portion (30), and an exhaust passage portion (39) of the exhaust duct (29) extends along an air discharge surface (27) and vertical walls (40, 41) of front and rear end portions of the fuel cell stack (11) while a pair of air discharge ports (42, 43) opens in front and rear end portions of the exhaust passage portion (39).