Abstract: The present invention discloses a fiber treatment agent containing an ester compound represented by the formula (1): R1—O-((EO)1—(PO)m)-(EO)n—CO—R2 ??(1) wherein, R1 represents a hydrocarbon group containing 8 to 24 carbon atoms; R2 represents an alkyl, alkenyl or cycloalkyl group having 7 to 23 carbon atoms; EO represents an ethyleneoxy group; PO represents a propyleneoxy group; 1 and n each represent an average reacted mole number of ethyleneoxy groups, 1 ranging from 0 to 15 and n ranging from 1 to 20; m represents an average reacted mole number of propyleneoxy groups, ranging from 0.5 to 20; and ((EO)1—(PO)m) and (EO)n are arranged in block in this order, while (EO)1 and (PO)m in ((EO)1—(PO)m) may be arranged at random or in block.