To accurately cut a hollow body of deformed cross section formed by a welding structure.

This circular saw cutter 1 cuts a workpiece W for a rear wheel shaft, and is provided with a vertically moving circular saw motor 7, a lower supporting member 15 of a floating supporting structure and an upper surface pressing member 20 symmetrically with respect to a width direction of the workpiece W. A rotating arm 9 for rotating the workpiece W on a cutting line is provided with clampers 11 for clamping a center part of the workpiece W at two portions and rotates in parallel with the cutting line. A pin 13 for center aligning is also installed at a detaching position. A projection 16 for supporting of the lower supporting member 15 and a projection 23 for pressing of the upper surface pressing member 20 are constituted of two projections away along the cutting line, respectively, to support a lower surface at substantially symmetrical positions on both sides of a center line of cutting ranges at end parts W2 of the workpiece W rotated to a cutting position and to press the upper surface.