Hollow-fiber membrane and hollow-fiber membrane module

A hollow-fiber membrane according to an aspect of the present disclosure contains a polytetrafluoroethylene or a modified polytetrafluoroethylene as a main component and has an average outer diameter of 1 mm or less and an average inner diameter of 0.5 mm or less. In a measurement of a heat of fusion of the polytetrafluoroethylene or the modified polytetrafluoroethylene with a differential scanning calorimeter, when the polytetrafluoroethylene or modified polytetrafluoroethylene is subjected to a first step of heating from room temperature to 365° C., a second step of cooling from 365° C. to 350° C., maintaining the temperature, subsequently cooling from 350° C. to 330° C., and further cooling from 330° C. to 305° C., and a third step of cooling from 305° C. to 245° C. at a rate of −50° C./min and subsequently heating from 245° C. to 365° C. at a rate of 10° C./min, a heat of fusion from 296° C. to 343° C. in the third step is 30.0 J/g or more and 45.0 J/g or less.