Abstract: A fan casing of window type air conditioner adapted to smoothen and form corners of outdoor casing in slow curvatures having convex and concave surfaces and to lengthen draft holes, thereby increasing amount of sucked air, reducing disturbance and resistance of air flow to decrease eddy current phenomenon and noises, and obtaining a broader accommodation spaces of compressor and the like on the concave surfaces, the fan casing comprising: convex surfaces formed facing the outdoor fan for increasing a suction amount of external air and simultaneously minimizing disturbance and reduction of air flow by increasing the length of the plurality of draft holes; and concave surfaces formed facing the condenser for obtaining a broaden accommodation space of the compressor and the like at a predetermined position at the convex surfaces and securing a larger suction area of external air.