To provide a cutting tool and a machining device capable of establishing an enhanced machining accuracy and machining quality of a work to be machined and of prolonging the lifetime of the cutting tool.

A motor, out of illustration, is put on, and its rotary shaft 3 is turned at approximately 12000 rpm. Approximately at the same time, an ultrasonic oscillator circuit is operated, and AC voltage of about 200 kHz is transmitted to a rotational side rotary transformer 17a through a stationary side rotary transformer 17b, and is further passed through a capacitor and impressed between silver electrodes on both sides of a piezoelectric element 2. From a nozzle the cooling water is given to a rotating cutter blade 1 in a disc shape and the work to be machined, not illustrated, and the glass of the work is cut or a groove is formed therein.