To provide a method for draining a thin steel sheet just after a tension leveler, by which draining is appropriately performed on a thin steel sheet just after straightened with a tension leveler, without generating a warpage on the thin steel sheet.

A draining device 20 in which upper and lower drain rolls 22 and an auxiliary roll 21 which is situated just before the drain rolls are integrated, is installed just after the tension leveler 11, the auxiliary roll 21 and the drain rolls 22 are moved vertically in conformity to the vertical movement of the final roll 12n of the tension leveler 11.