To provide a device machining a narrow spot such as an inner face of a pipe and a machining method using it.

The machining device 1 is provided with a main body 2, a driving means 3 installed in the main body 2, a slender cylindrical insert 4 extending from the main body 2, a rotary blade 5 rotatably-installed in a bearing 4a attached to the tip of the insert 4, and a driving force transmission mechanism 6 comprising an endless belt located along inside the insert 4. Pulling a control lever 8 actuates the driving means 3, then its driving force is transmitted to the rotary blade 5 via the driving force transmission mechanism 6.