Device for forming expanded hole section

A hold expansion forming device comprising:

• a cutting portion main body formed to have a diameter for the cutting portion main body to be housed in a joint hole (61) and including a cutting blade tool movable in a range between a housed position at which a blade is housed within the diameter of the cutting portion main body and an extended position at which the blade projects out of the diameter of the cutting portion main body, an advancing and retracting member that is constructed to move in an axial direction by an external force and rotate about an axis of the advancing and retracting member, and a link mechanism that converts an advancing and retracting movement of the advancing and retracting member into a rotational movement of the cutting blade tool;
• a tip portion bearing that is provided on a tip end of the cutting portion main body and serves as a tip end side bearing when being housed in an inner portion, of the joint hole;
• and
• a torque transmitting element to transmit a torque about the axis of the advancing and retracting member to the advancing and retracting member.