PURPOSE: To cut smoothly the billets of respective strands in good order and to decrease installation cost by using a cutter commonly for the plural strands, selecting the strand to be cut next and emitting a moving command.

CONSTITUTION: A speed detector 102 of a cutter detects the speed of the cutter during its movement and feeds a signal to a position control device 107. A position detector 103 of the cutter detects the traveling and traversing positions of the cutter from an origin 4 and transmits the signal to the device 107. A length measuring device 104 converts technically the count value of a pulse generator provided to a measuring roll 3 to measure the moving distance of the billet and is reset by a signal for starting cutting of the billet. A speed detector 105 and a billet width measuring device feed the signals obtd. at respective detection ends 100 and 101 to the device 107. The device 107 obtains the signal for starting and completion of cutting from the cutter, and the information on the length of the billet intended to be cut, etc. in addition to the above-mentioned signal. The device 107 selects a strand in accordance with said signals, determines the timing for cutting and outputs the command for traversing and traveling position, the command for the timing for cutting, etc.