PURPOSE: To make a main guide post or the like relatively smaller than the size of a cutting head by connecting a stanchion erected near the main guide post integrally with the main guide post.

CONSTITUTION: A guide column device 9 guiding a cutting head in the vertical direction is provided with a main guide post 59 erected on the right side sub- base and a sub-guide post 61 erected on the left side sub-base, and stanchions 63R, 63L are erected on the right and left sides behind and near both posts 59, 61 respectively. Lower sections of the posts 59, 61 are connected to upper sections of the stanchions 63R, 63L respectively with connecting members, and the upper connecting members 67R, 67L are integrally connected to each other via an intermediate connecting member 69. Accordingly, the posts 59, 61 are not deflected in the longitudinal direction by the unbalanced load due to the longitudinal movement of the cutting head against the posts 59, 61, and the lateral deflection is prevented by the connecting member.