A cowl top 7 includes a tubular peripheral wall 71 provided above a dash panel 104, with its upper portion 73 extending along a lower edge of a front wind shield 105, the upper portion 73 of the peripheral wall 71 having a front communication aperture 75 and a rear communication aperture 76 formed for air communication between atmosphere and the interior of the tubular peripheral wall 71, and a diluter 6 includes an air inlet aperture area 62 communicating with the interior of an air discharge duct 4, an air outlet aperture area 63 communicating with the interior of the tubular peripheral wall 71, and a dilution chamber 61 made up to introduce fuel gas discharged from a fuel cell stack 3, dilute introduced fuel gas with air introduced through the air inlet aperture area 62, and discharge diluted fuel gas through the air outlet aperture area 63.