PURPOSE: To obtain efficient finish cut of a paper tube by providing a cutting- position detecting means for the paper tube, a migration distance detecting means for a round blade holder, and a means to determine the timing of actuation of a returning device through setting of a timer.

CONSTITUTION: A detector, which detects the position of the tip of a paper tube 9, is arranged on the extension of a migration route (on the downstream side) of a cutting core 8, in such a manner that it ban be positioned along the migration route of the paper tube 9. Following a detection signal by the detector, a cylinder 61 of an approaching/receding device 6 operates so as to push a round blade 4 against the paper tube 9. In this connection, when a lever detector 101a, which is a means 101 to determine the timing of a start of a cylinder 73, is activated by a second lever 72 of a returning device 7, the cylinder 61 draws in a piston rod so that the round blade 4 recedes from the paper tube 9, and then both returning device 7 and a retracting device operate, so that both round blade 4 and cutting core 8 return to their initial positions. With this contrivance, the paper tube 9 can be finish-cut to a prescribed length one after the other, thereby drastically enhancing the work efficiency.