PURPOSE: To make it possible to cut a plate material on travelling widthwise at a high speed with a high degree of accuracy by use of a misscut system drum type flying shear, by providing such an arrangement that a planetary gear in a planet gear mechanism is attached to at least either one of upper and lower drums.

CONSTITUTION: Pinions 22 fitted on the left end parts of upper end lower drum shafts 3 in a shear, are meshed with the outer teeth 17 of a ring gear 19, and a planetary gear 23 attached to the right end side of a lower drum 9 is meshed with the inner teeth 18 of the gear 19 so that a planetary gear mechanism is constituted on the lower drum side. Accordingly, a phase shift is obtained between the meshing positions of upper and lower cutting edges 1, 8. Accordingly, with the repetition of misscut until the meshing positions coincides with each other, a severing operation may be made in such a condition that the rotational speed is accelerated. Thus, there is a no risk of abrasion and twice cuttings as experienced with the conventional device, and on-travel cutting may be made at a high speed with a high degree of accuracy.