To provide nanofibers having less spread of single fiber fineness values that can be used in wide applications without limitation to a fiber and the shape of a fiber product.

The aggregate of the nanofibers is made of a polyester selected from a polylactic acid, a polybutylene terephthalate, a polytrimethylene terephthalate and a polyethylene glycol-copolyester. The single fiber fineness by number average is in a range from 1×10-7 to 2×10-4 dtex, and single fibers of 60% or more in fineness ratio have single fiber fineness in a range from 1×10-7 to 2×10-4 dtex.