To improve a product quality and extend the life of a tool by attempting proper processing condition by more accurately grasping the load when form-rolling a screw.

More accurate load for form-rolling the screw can be obtained by measuring the strain of a tension bar 28 where the strain is caused by remarkably reflecting an opposing force at the time of form-rolling the screw by a strain gauge 29, and by obtaining the load at the time of form-rolling the screw based on this measured value. Furthermore, the position where the strain gauge 29 is mounted is not restricted to this tension bar 28 but can be mounted to the other part where the strain is caused by remarkably reflecting the opposing force at the time of form-rolling the screw. By measuring the strain at this part and obtaining the load at the time of form-rolling the screw based on the measured value, the value of the load at the time of form-rolling the screw can be obtained more precisely.