In a cutting insert of the invention, a protruded portion formed on an upper surface lying more inward than a breaker groove along a corner comprises a breaker projection adjacentmost to the corner; a breaker wall face formed connectedly with the breaker projection so as to project more upward than the breaker projection; and a breaker side face formed connectedly with the breaker wall face. The breaker wall face is formed to have a smaller width toward the projecting direction of the breaker wall face, and inclined to have a higher position as it departs from the corner. The breaker side face is formed to have a larger width as it departs from the corner. The height of the breaker projection is not more than half of the height of the top of the breaker wall face, and is lower than the height of the cutting edge along the corner. A cutting method using a cutting tool comprising the cutting insert is also provided.