Indexable rotary cutting tool

One kind of insert which is detachably mounted to a rotary indexable cutting tool, wherein the upper surface includes a portion having a cutting edge on the ridge line, the lower surface portion, a side portion, and a stopper with a central screw hole angle edge of each corner portion is provided at an acute angle, and a rear cutting edge includes the corner ridge line on both sides of the edge of the sub cutting edge and the peripheral cutting edge, a minor cutting edge and the outer peripheral edge has a different clearance angle, angle of cutting edge a face having a rake angle of the variable angle continuously changes within a range from a minor cutting edge side to the outer peripheral cutting edge side of the upper end of the outer circumferential edge portion formed with a recess defining its length.