Pressure and frictional stress acting on the ripper point surface have been directly measured in the actual rock ripping process using stress sensors embedded in the top part of the ripper point. In the case of ripping sand stone ground, applied stresses are relatively low but sometimes increase rapidly, unless the traction force is constant. In the case of ripping conglomerate ground, large stress is applied to the top of the point surface and changes in proportion with the traction force. Point surface temperature has been also measured using an embedded temperature sensor. The temperature increases intermittently during the ripping process.