To improve precision of a shape control in the steel plate width direction by arranged a displacement gauge on the surface and rear sides of the steel plate, finding a differential of output signals for eliminating a drift factor based on a temperature change of the steel plate, and controlling the shape of the steel plate.

Signals including drift factors from displacement gauges 2, 3 on the surface and rear sides are outputted as a surface side output voltage (VS) and a rear side output voltage (VR) via a converter 6 to a displacement conversion unit (temperature correction circuit), and a distance between the surface and rear side displacement gauges 2, 3 measured by means of range finders 16, 17 is inputted to the displacement converting unit. The displacement converting unit eliminates a drift factor without respect to a steel plate temperature by performing computing on the basis of a specific formula. A differential between a surface side displacement gauge 2 signal, from which a temperature drift factor of the displacement gauge 2 is eliminated, from the displacement converting unit and a target value is found by means of a differentiator, and subsequently, it is passed through a feedback gain circuit, and then, through a phase compensation circuit after proportional integral is carried out in a comparison circuit and an integrator, so as to generate a drive control signal.