Thin steel strip is passed through a pinch roll stand comprising pinch rolls to a rolling mill comprising a pair of work rolls and upper and lower backing rolls. A flexible section may be selectively positioned to reduce an amount of strain in the high strain region when subjected to the applied stress during use to inhibit or prevent fracturing in the high strain region. Furthermore, because a collective control is executed on the sense amplifiers to be activated, instead of individually controlling the sense amplifiers to be activated, the circuit scale of the sense-amplifier control circuit can be reduced. The control unit for controlling the detection board so that the detection board is placed in a predetermined temperature state. This erasure radiation can have both a first and a second intensity, the first intensity being larger than the second intensity.