The object of the invention is to stably spray cutting fluid in a good mist form, when cutting fluid and air are supplied from the surrounding area and cutting fluid is sprayed in a mist form from the tip end section of a rotary cutting tool. The rotary cutter of the present invention sequentially feeds a mixture of cutting fluid and air through a supply pipe 4, first supply path b in a cover 3, second supply paths c, d in a chuck 2, a hollow center cavity (front throttle chamber d, throttle 24a, and rear throttle chamber e) in the chuck, and a third supply path g in a rotary cutting tool 1. The first supply path and second supply path are intermittently connected when the respective openings thereof face each other as the cover and chuck turn relative to each other; the second supply path sprays fluid toward the throttle; the front throttle chamber is formed such the diameter thereof expands from the second supply path; the throttle is formed such that the diameter thereof is less than the smallest diameter of the second supply path; the rear throttle chamber is formed by the rear end surface of the rotary cutting tool and the inner conical surface on the down-flow side of the throttle when that rear end surface and inner conical surface on the down-flow side come in close contact with each other; and the front throttle chamber is formed such that the capacity thereof is greater than that of the rear throttle chamber.