To vertically cut a bamboo material with good work efficiency and increase the number of vertical cuts as necessary without declining the work efficiency so as to be suitable for biomass use accompanied by conversion to chips and powder materials.

The bamboo material 1 is supplied between a pair of pressurizing members 2, 3 longitudinally, and by revolution or rotation in one direction of at least one of the pressurizing members 2, 3, the supplied bamboo material 1 is received and crushed between the pressurized members 2, 3 by pressing force and/or biting force. While cracks in the longitudinal direction are produced at a plurality of portions in the circumferential direction, transfer to the supply opposite side along with further flattening is continuously performed. The bamboo material 1 is ruptured at the crushed cracks to achieve a vertically cut state, and this is continued to subsequent portions, so as to send out a plurality of vertically cut pieces 5.