Apparatus for tightening string

A string tightening device comprising:

• a base where a first locking portion is provided;
• a lower rotation member that is disposed in the base and moves a predetermined distance in a direction of separation from the base or the opposite direction thereof;
• and
• an upper rotation member coupled to the lower rotation member, including a second locking portion corresponding to the first locking portion, and rotating only in one direction when the first locking portion and the second locking portion are closely attached,
• wherein the lower rotation member or the upper rotation member is provided with an inner housing portion where a string is wound,
• wherein the base and the upper rotation member comprise a rotation unit position adjusting portion provided in a portion where the base and the upper rotation member face each other and configured to maintain the first locking portion and the second locking portion in a closely attached state or in a separated state,
• wherein the rotation unit position adjusting portion is formed of a first protrusion portion provided in the base and a second protrusion portion provided in the upper rotation member to be adjacent to the first protrusion portion,
• wherein the base comprises an outer housing portion formed in the shape of a cylinder and the outer housing portion is provided with a first projection portion that is concave along an internal circumferential direction of a lower end portion thereof,
• wherein the lower rotation member comprises a second projection portion which is caught by the first projection portion and thus of which movement is limited to a predetermined distance or less in a direction parallel to a rotation axis of the lower rotation member,
• wherein the first projection portion has a first surface facing a second surface of the second projection portion, and
• wherein the upper rotation member is configured to move away from the base in the direction parallel to the rotation axis and the second protrusion portion is configured to go over the first protrusion portion, thereafter the first surface of the first projection portion and the second surface of the second projection portion contact to each other and unwinding state is maintained.