The present invention provides a cutting insert and a cutting tool used with the same. A tool body includes at least one seating surface and a threaded hole extending as slanted with respect to the seating surface. At least one cutting insert having a mounting hole passing therethrough is removably secured on the seating surface. A screw passes through the mounting hole and is fastened to the threaded hole, thereby removably securing the cutting insert to the tool body. A wall surface of the mounting hole contacts a head of the screw about at least one first contact portion and at least one second contact portion. The first contact portion is formed at a level different from that of the second contact portion along a longitudinal axis of the mounting hole. Contact angles at the first contact portions and the second contact portions are different from each other.