To automatically detect the tip part of a hot-rolled or cold-rolled coil being subjected to band-cut treatment accurately and to save power and improve a working efficiency by arranging a tip detector between a cradle roll and a coil ovener.

For example, a coil tip detector 18 such as a laser displacement meter is installed between a cradle roll 6 and a coil ovener 4. Then, a coil 7 is placed on a roll so that a tip part 7a of the steel plate coil 7 is located near the upper part of an upper guide table 4a on the coil ovener 4, the roll 6 is inverted when the upper guide table 4a lightly touches the coil 7, and the coil tip part 7a is rotated in the direction of the roll 6 (counterclockwise) from the upper guide table 4a. While the roll 6 is being rotated, a distance between the surface of the coil 7 and a tip detector 18 is measured, the measurement data are filtered by an amplifier and is outputted as a tip detection signal.