The present invention provides the nonionic surfactant represented by the formula (1): €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒR-O-(PO) m -(EO) n -H€ƒ€ƒ€ƒ€ƒ€ƒ(1) wherein, R represents a saturated linear-chain hydrocarbon group having 8 to 18 carbon atoms, and n-octyl groups are 20 to 80% by mole of the saturated linear-chain hydrocarbon groups, n-decyl groups are 0 to 10% by mole of the saturated linear-chain hydrocarbon groups, and saturated linear-chain hydrocarbon groups having 12 to 18 carbon atoms are 20 to 80% by mole of the saturated linear-chain hydrocarbon groups； PO represents a propyleneoxy group； EO represents an ethyleneoxy group； m represents an average addition mole number of propyleneoxy groups ranging from 0.1 to 5； n represents an average addition mole number of ethyleneoxy groups ranging from 0.5 to 20； and (PO) m and (EO) n are bonded as blocks in this order.
