A machining assistance system for assisting a machining apparatus, the machining apparatus including: a workpiece retaining tool configured to retain a workpiece; a machining unit configured to machine the workpiece retained by the workpiece retaining tool by driving a working tool; and a machining control device configured to perform control of moving the machining unit relative to the workpiece retaining tool to position the working tool at a machining position, the machining assistance system comprising: a workpiece supporting force generating unit configured to generate workpiece supporting force against machining reaction force that is exerted on a machining portion of the workpiece by the working tool; a supporting device configured to move the workpiece supporting force generating unit while supporting the workpiece supporting force generating unit; and a workpiece supporting force control device configured to control operation of the workpiece supporting force generating unit and operation of the supporting device based on machining reaction force related data related to the machining reaction force and machining position related data related to the machining position of the working tool, such that the workpiece supporting force generating unit exerts the workpiece supporting force on the workpiece against the machining reaction force, characterized in that the machining unit is configured to perform machining of the workpiece retained by the workpiece retaining tool by causing a columnar or discoid rotating tool with a cutting edge or grinding stone formed on its peripheral surface or distal end surface to rotate about a central axis of the rotating tool, the workpiece supporting force generating unit includes a columnar rotary body and a rotation driver that causes the rotary body to rotate about a central axis of the rotary body, and the workpiece supporting force control device is configured to, based on the machining reaction force related data and the machining position related data and by using the supporting device, perform: control of an orientation and a position of the workpiece supporting force generating unit, such that the central axis of the rotary body is parallel to the central axis of the rotating tool, and the rotary body exerts pushing force on the workpiece against cutting reaction force that is exerted on the workpiece by the rotating tool; and control of operation of the rotation driver to cause the rotary body to rotate, such that a rotational torque is exerted on the workpiece against a torque that is generated by the cutting reaction force. a workpiece supporting force generating unit configured to generate workpiece supporting force against machining reaction force that is exerted on a machining portion of the workpiece by the working tool; a supporting device configured to move the workpiece supporting force generating unit while supporting the workpiece supporting force generating unit; and a workpiece supporting force control device configured to control operation of the workpiece supporting force generating unit and operation of the supporting device based on machining reaction force related data related to the machining reaction force and machining position related data related to the machining position of the working tool, such that the workpiece supporting force generating unit exerts the workpiece supporting force on the workpiece against the machining reaction force, characterized in that the machining unit is configured to perform machining of the workpiece retained by the workpiece retaining tool by causing a columnar or discoid rotating tool with a cutting edge or grinding stone formed on its peripheral surface or distal end surface to rotate about a central axis of the rotating tool, the workpiece supporting force generating unit includes a columnar rotary body and a rotation driver that causes the rotary body to rotate about a central axis of the rotary body, and the workpiece supporting force control device is configured to, based on the machining reaction force related data and the machining position related data and by using the supporting device, perform: control of an orientation and a position of the workpiece supporting force generating unit, such that the central axis of the rotary body is parallel to the central axis of the rotating tool, and the rotary body exerts pushing force on the workpiece against cutting reaction force that is exerted on the workpiece by the rotating tool; and control of operation of the rotation driver to cause the rotary body to rotate, such that a rotational torque is exerted on the workpiece against a torque that is generated by the cutting reaction force. control of an orientation and a position of the workpiece supporting force generating unit, such that the central axis of the rotary body is parallel to the central axis of the rotating tool, and the rotary body exerts pushing force on the workpiece against cutting reaction force that is exerted on the workpiece by the rotating tool; and control of operation of the rotation driver to cause the rotary body to rotate, such that a rotational torque is exerted on the workpiece against a torque that is generated by the cutting reaction force.