To provide a cutting working device capable of facilitating assembling work by making it in a simple structure, reducing noise and vibration and facilitating restoration in case of an emergency stop, power failure, etc.

A connecting shaft 14 is moved to the rear side by a cylinder mechanism 17 in carrying out cutting work by installing a rotary tool holder 13 on a main spindle 12 of the cutting working device 10. The connecting shaft 14 is supported through a bush 19 by the supporting mechanism 20. It is possible to mill a work piece by a tool 13a, etc. by rotating the main spindle 12 at high speed by a motor 15 for the main spindle. The connecting shaft 14 is not connected to the main spindle 12 and does not make contact with the main spindle 12, either. The connecting shaft 14 is supported through the bush 19 by the supporting mechanism 20 and a rear end is supported by a bearing 24.