To provide a cutting tool mounting and demounting device of a simple structure capable of easily mounting and demounting a cutting tool to a motor- driven tool or the like.

In this cutting tool mounting and demounting device for fixing and connecting the cutting tool 12 having a connecting part 18 on its rear end, a cylindrical part 19 having a recessed connection part 20 for inserting the connecting part is mounted, a through hole 22 radially penetrated through a main body having a shank 14 engaged with a chatter of the motor-driven tool or the like on its rear end, and the cylindrical part 19 for storing a steel ball 24 as a connecting member fitted and fixed to a recessed part formed on the cutting tool, and a hole 42 for storing a steel ball 44 holding an extruding member energized by a spring 40 on a storing position are formed, and an operating sleeve axially slidably formed on an outer periphery, having the shape to inwardly press the steel balls, and energized in a fixed direction by a spring is mounted. When the sleeve is pressed down against the energizing force of the spring, and the cutting tool is pressed in the connection recessed part 22, the steel ball is fitted in the recessed part 26 for fixing, of the cutting tool, and fixed.