The present invention aims at supplying a fiber-processing agent that can suppress scum accumulation in whirling air spinning to a large extent and thereby assure good high-speed spinning performance. The present invention uses a fiber-processing agent for whirling air spinning having a kinetic viscosity at 30°C of 1 x 10 -6 to 100 x 10 -6 m 2 /s; wherein the fiber-processing agent comprises one, two or more of the following lubricant (A), the following lubricant (B) and the following lubricant (C); wherein: Lubricant (A) is an aliphatic ester compound of carbon number 5-70; Lubricant (B) is a linear polyorganosiloxane, having a kinetic viscosity at 30°C of 5 x 10 -6 to 100 x 10 -6 m 2 /s; and Lubricant (C) is a mineral oil, having a kinetic viscosity at 30°C of 5 x 10 -6 to 100 x 10 -6 m 2 /s.