A soft back-up pin state checking device including a soft back-up pin formed of a bottom-side holder portion, and a top-side soft pin portion which is held by the holder portion in an exchangeable manner. A ring-shaped background portion which is possible to be distinguished from the soft pin portion and be recognized using image processing is provided on a top end surface of a cylindrical fitting portion which is outside of an outer circumference of the soft pin portion in the holder portion of the soft back-up pin.