An insert comprises an insert main body having an upper surface and a plurality of side surfaces, a cutting edge located between both ends of a ridge which is between at least one side surface among the side surfaces and the upper surface, a high-positioned portion located at one end of the ridge, and a low-positioned portion located lower in the thickness direction of the insert main body than the high-positioned portion and located at the other end of the ridge. The cutting edge comprises a first flat cutting edge having substantially the same height as the high-positioned portion, and a tilted cutting edge having a height decreasing from the high-positioned portion toward the low-positioned portion. On at least the one side surface, at least one groove extends from the side surface to the upper surface to divide the cutting edge by the groove, and at least the one groove is formed at a region including an intersection of a first extension line formed by imaginarily extending the first flat cutting edge with a second extension line formed by imaginarily extending the tilted cutting edge. This enables reduction in the occurrence of vibration during cutting, and the chipping.