An elongation rolling control method is provided which can manufacture a hollow shell of high dimensional accuracy and can suppress rolling problems. It is an elongation rolling control method in which the groove bottom wall thickness of a hollow shell P in stand #1 having an ultrasonic wall thickness wall gauge 1 installed between it and stand #2 is measured, the outer diameter of a mandrel bar B is calculated based on the set value of the roll gap in stand #1 and the groove bottom wall thickness of the hollow shell P, the location in the lengthwise direction of the mandrel bar B for which the outer diameter was calculated is determined based on positional information on a bar retainer BR, the distribution in the lengthwise direction of the outer diameter of the mandrel bar is calculated by repeating the above steps, the location in the lengthwise direction of the mandrel bar which contacts the hollow shell in a subsequent stand is determined based on positional information on the bar retainer, and the roll gap in the subsequent stand is set based on the outer diameter of the determined location in the lengthwise direction of the mandrel bar.