A nonionic surfactant that is environmentally friendly, has excellent surface active power (emulsifying power and solubilizing power), and is capable of stably maintaining the excellent surface active power for a long time is provided. A nonionic surfactant of the present invention contains polyglycerol monoether represented by the formula (1), wherein a ring Z represents a condensed ring of an aromatic hydrocarbon ring having 6 to 14 carbon atoms and a 3 to 6-membered heterocycle containing an oxygen atom as a heteroatom； R 1 is a substituent bonded to the ring Z and represents an aliphatic hydrocarbon group having 14 to 25 carbon atoms； the ring Z optionally has one or more substituents other than R 1 ； and n is an average number of monomers of glycerol and represents 2 to 20.
