The characteristics are investigated experimentally for the purpose of detecting tool wear and fracture by variations in cutting force. In this experiment, hardened steel (JIS SKD 11) is turned with a ceramic tool under finish machining condition. The main results obtained are as follows. (1) The influences of the shape of cutting edge and cutting condition on cutting force are clarified. (2) The ratio of radial force to feed force increases linearly with respect to tool flank wear width (V_B). (3) When plastic deformation of cutting edge precedes fracture occurrence, the occurrence can be predicted by the increase in radial or feed force caused by the deformation.