PURPOSE: To hold a cutting machine easily and securely at a desired cutting part by holding said cutting machine on an object to be cut via a magnet chuck base by means of a holding magnet in a ship disjointing cutting unit.

CONSTITUTION: A magnet chuck base 24 is placed on an iron board 29, so as to be correspondent with a defined cutting line L while considering a clearance M between the cutter 14 of a cutting machine 1 and the base 24, and an electromagnet 28 is excited to firmly hold the plate 29. Then, the cutter 1 is placed on the magnet chuck base 24 in such a way that one side of its lower part is joined to a positioning rib 26, and an electromagnet 27 is excited to firmly hold the machine 1. After that, a cutter 14 is rotated by means of a hydraulic motor 11 while being lowered by the rotation of a handle 21, to cut the iron board 29, and advances while cutting in the axial direction by the rotation of a handle 9. Thereby, the cutting machine can be set and held with respect to a desired cutting part easily and securely while eliminating the danger of fire, etc.