Disclosed is a device for heat-treating an inner surface of a braid for reinforcing a hollow fiber membrane for water treatment with a temperature control structure. The device includes a heating core; a heater coupled to the heating core; a temperature sensor passing through the heater; a cylindrical housing through which the heater and the sensor pass; a heat shield tube placed between the heating core and the housing and coupled to the heating core; a clamping nut connecting the heat shield tube and the housing; a mounting board on which a lower portion of the housing is fixed; and a temperature controller.