A strip thickness controller for a rolling mill, which is capable of reducing a delivery-side strip thickness deviation due to an eccentricity of a backup roll even in a rolling mill incapable of easily performing a kiss-roll. The strip thickness controller provides with a thickness gauge, provided in a position spaced a distance shorter than a circumference of each of backup rolls on a delivery side of the mill, for detecting a strip thickness deviation from a set value, an angle detecting unit for outputting a rotational angle detection signal at every equally-segmented portion when an angle of one rotation of the backup roll is, with “n” being a positive integer, segmented equally by “n”, a calculating unit for calculating a forward slip of the mill at a point of time when a first rotational angle detection signals outputted, and calculating, based on the forward slip and the circumference of the backup roll, a delivery-side strip length of the rolling mill which corresponds to one rotation of the backup roll and a delaying unit for delaying a strip thickness deviation signal of the thickness gauge by a strip transfer time corresponding to a difference between the delivery-side strip length calculated by the calculating unit and a distance of the thickness gauge from the rolling mill.