A rotary cutter having: a chuck that grips and holds a rotary cutting tool, and is fastened to a main rotating shaft; and a cover having a cylindrical section that covers and comes in close contact around the circumference of part of the outer peripheral surface of the chuck such that sliding movement is possible, and is supported such that rotation is not possible; wherein the cover has a first supply path (b); the chuck has a second supply path and a hollow center cavity; the rotary cutting tool has a third supply path (g) that is formed such that openings on the rear end surface and a tip end section are connected; the first supply path (b), the second supply path, the hollow center cavity and the third supply path (g) are fluidly connected, characterized in that a throttle is formed at a position on the axis of rotation inside the hollow center cavity such that the throttle divides the hollow center cavity into a front throttle chamber (e) that is connected to the second supply path and a rear throttle chamber (f) that is connected to the third supply path (g); the front throttle chamber (e) and the rear throttle chamber (f) have diameters that constrict in the direction toward the throttle; and the second supply path is oriented toward the throttle, such that a fluid-air mixture of cutting fluid and air fed to the first supply path (b) passes in order through the first supply path (b), the second supply path, the hollow center cavity and the third supply path (g) to the tip end section, and the fluid-air mixture of cutting fluid and air is sprayed in mist form from the tip end section of the rotary cutting tool. a chuck that grips and holds a rotary cutting tool, and is fastened to a main rotating shaft; and a cover having a cylindrical section that covers and comes in close contact around the circumference of part of the outer peripheral surface of the chuck such that sliding movement is possible, and is supported such that rotation is not possible; wherein the cover has a first supply path (b); the chuck has a second supply path and a hollow center cavity; the rotary cutting tool has a third supply path (g) that is formed such that openings on the rear end surface and a tip end section are connected; the first supply path (b), the second supply path, the hollow center cavity and the third supply path (g) are fluidly connected, characterized in that a throttle is formed at a position on the axis of rotation inside the hollow center cavity such that the throttle divides the hollow center cavity into a front throttle chamber (e) that is connected to the second supply path and a rear throttle chamber (f) that is connected to the third supply path (g); the front throttle chamber (e) and the rear throttle chamber (f) have diameters that constrict in the direction toward the throttle; and the second supply path is oriented toward the throttle, such that a fluid-air mixture of cutting fluid and air fed to the first supply path (b) passes in order through the first supply path (b), the second supply path, the hollow center cavity and the third supply path (g) to the tip end section, and the fluid-air mixture of cutting fluid and air is sprayed in mist form from the tip end section of the rotary cutting tool.