PURPOSE: To half cut a material reliably even when the length of the material is varied, by providing the position detecting signal of a moving rolling material to an addition and subtraction counter.

CONSTITUTION: When the tip of a rolling material reaches to first detector 4 provided at the material feeding side of a cropshare 3, a detection signal is produced to close a contact 11 while to open a gate 12 and to provide the clock pulse from a generating device 7 to an adding counter 9. When a rolling material 1 passes in front of the first detector 4, said counter is disabled and its content is written into a subtraction counter 10. Thereafter when the leading edge of an intermediate rolling material is detected by a second counter 5, a contact 13 is closed while gate 14 is opened and a clock pulse having the frequency two times that of the adding time is provided to the subtraction counter 10 and when the content of the subtraction counter is equal to the level set by a setter 17 a cut command signal Pc is provided from a comparator 18 to the crosphare 3.