An outdoor unit of an air conditioner comprising: a base panel; a front panel erected on a front end of the base panel and having a through hole formed therein; an orifice fitted to the through hole; a fan placed behind the through hole and having at least a portion accommodated inside the orifice; and a heat exchanger placed on an edge of a rear side of the base panel, wherein a front-to-back width of one side end of the orifice is less than that of the other side end of the orifice, wherein the heat exchanger comprises: a short side extending along one side end of the base panel; and a long side bent from a rear end of the short side and extending along a rear end of the base panel, wherein one end of the orifice is adjacent to the short side, and characterized in that the front-to-back width of the orifice increases linearly from one end of the orifice to a center of the orifice, and is formed to be parallel to the front surface of the orifice from the center of the orifice to the other end of the orifice, wherein a fastening sleeve extends at the edge of the through hole, wherein at least a portion of the fastening sleeve is bent to a front side of the front panel, wherein the outdoor unit further comprises: misassembly prevention ribs (1391, 1392) formed at upper and lower ends of a back surface of the front panel, respectively; and misassembly prevention grooves (1224, 1225) formed in upper and lower ends of the fastening sleeve, respectively, to accommodate the misassembly prevention ribs (1391, 1392). a base panel; a front panel erected on a front end of the base panel and having a through hole formed therein; an orifice fitted to the through hole; a fan placed behind the through hole and having at least a portion accommodated inside the orifice; and a heat exchanger placed on an edge of a rear side of the base panel, wherein a front-to-back width of one side end of the orifice is less than that of the other side end of the orifice, wherein the heat exchanger comprises: a short side extending along one side end of the base panel; and a long side bent from a rear end of the short side and extending along a rear end of the base panel, wherein one end of the orifice is adjacent to the short side, and characterized in that the front-to-back width of the orifice increases linearly from one end of the orifice to a center of the orifice, and is formed to be parallel to the front surface of the orifice from the center of the orifice to the other end of the orifice, wherein a fastening sleeve extends at the edge of the through hole, wherein at least a portion of the fastening sleeve is bent to a front side of the front panel, wherein the outdoor unit further comprises: misassembly prevention ribs (1391, 1392) formed at upper and lower ends of a back surface of the front panel, respectively; and misassembly prevention grooves (1224, 1225) formed in upper and lower ends of the fastening sleeve, respectively, to accommodate the misassembly prevention ribs (1391, 1392). a short side extending along one side end of the base panel; and a long side bent from a rear end of the short side and extending along a rear end of the base panel, wherein one end of the orifice is adjacent to the short side, and characterized in that the front-to-back width of the orifice increases linearly from one end of the orifice to a center of the orifice, and is formed to be parallel to the front surface of the orifice from the center of the orifice to the other end of the orifice, wherein a fastening sleeve extends at the edge of the through hole, wherein at least a portion of the fastening sleeve is bent to a front side of the front panel, wherein the outdoor unit further comprises: misassembly prevention ribs (1391, 1392) formed at upper and lower ends of a back surface of the front panel, respectively; and misassembly prevention grooves (1224, 1225) formed in upper and lower ends of the fastening sleeve, respectively, to accommodate the misassembly prevention ribs (1391, 1392). misassembly prevention ribs (1391, 1392) formed at upper and lower ends of a back surface of the front panel, respectively; and misassembly prevention grooves (1224, 1225) formed in upper and lower ends of the fastening sleeve, respectively, to accommodate the misassembly prevention ribs (1391, 1392).