An outdoor unit of an air conditioner comprising: a housing including an outlet; a fan disposed inside the housing; and a guide configured to guide air flowing by the fan, wherein the guide includes: an inflow portion provided to guide air introduced into the housing to the fan; and a diffuser extending from the inflow portion to guide air passing through the fan to the outlet, wherein the inflow portion includes: a duct connected to the diffuser; a bell mouth disposed on an upstream side of the duct and configured such that, seen in a front view of the fan, a width of an inlet end of the bell mouth is wider than a width of an outlet end of the bell mouth; and a plurality of guide vanes (80, 380) formed on an inner surface of the bell mouth and configured to guide a flow direction of air introduced through the bell mouth into the fan, wherein each guide vane has a first end (80b, 380b) and a second end (80a, 380a) and each guide vane is configured to be curved from the first end (80b, 380b) that is an arbitrary point on the inner surface of the bell mouth to the second end (80a, 380a) that is a point on the inner surface of the bell mouth close to the outlet end of the bell mouth, characterized in that for each guide vane, when a distance of a straight line connecting the first end (80b, 380b) and the second end (80a, 380a) of the guide vane is referred to as a length of the guide vane and when an angle between an imaginary extension line extending from the second end (80a, 380a) of the guide vane and a perpendicular line directed to the second end (80a, 380a) of the guide vane from a center line passing through a rotation center of the fan, is referred to as an outlet angle of the guide vane, the length varies along the circumference of the bell mouth and the outlet angle varies according to the length, such that the plurality of guide vanes (80, 380) is configured to have a longer length as the outlet angle increases. a housing including an outlet; a fan disposed inside the housing; and a guide configured to guide air flowing by the fan, wherein the guide includes: an inflow portion provided to guide air introduced into the housing to the fan; and a diffuser extending from the inflow portion to guide air passing through the fan to the outlet, an inflow portion provided to guide air introduced into the housing to the fan; and a diffuser extending from the inflow portion to guide air passing through the fan to the outlet, wherein the inflow portion includes: a duct connected to the diffuser; a bell mouth disposed on an upstream side of the duct and configured such that, seen in a front view of the fan, a width of an inlet end of the bell mouth is wider than a width of an outlet end of the bell mouth; and a plurality of guide vanes (80, 380) formed on an inner surface of the bell mouth and configured to guide a flow direction of air introduced through the bell mouth into the fan, a duct connected to the diffuser; a bell mouth disposed on an upstream side of the duct and configured such that, seen in a front view of the fan, a width of an inlet end of the bell mouth is wider than a width of an outlet end of the bell mouth; and a plurality of guide vanes (80, 380) formed on an inner surface of the bell mouth and configured to guide a flow direction of air introduced through the bell mouth into the fan, wherein each guide vane has a first end (80b, 380b) and a second end (80a, 380a) and each guide vane is configured to be curved from the first end (80b, 380b) that is an arbitrary point on the inner surface of the bell mouth to the second end (80a, 380a) that is a point on the inner surface of the bell mouth close to the outlet end of the bell mouth, characterized in that for each guide vane, when a distance of a straight line connecting the first end (80b, 380b) and the second end (80a, 380a) of the guide vane is referred to as a length of the guide vane and when an angle between an imaginary extension line extending from the second end (80a, 380a) of the guide vane and a perpendicular line directed to the second end (80a, 380a) of the guide vane from a center line passing through a rotation center of the fan, is referred to as an outlet angle of the guide vane, the length varies along the circumference of the bell mouth and the outlet angle varies according to the length, such that the plurality of guide vanes (80, 380) is configured to have a longer length as the outlet angle increases.