The present invention provides the nonionic surfactant represented by the formula (1): R—O—(PO)m-(EO)n—H  (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.