A flexible tube insertion apparatus (10) includes an insertion section (40), a stiffness variable unit (50), an advance and retreat detection unit (60), a controller (121), and a drive (70). The controller (121) controls a stiffness of the stiffness variable unit (50) to be a stiffness that makes the insertion section (40) passively bendable when the advance and retreat detection unit (60) has detected an advance of the insertion section (40). The controller (121) controls the stiffness of the stiffness variable unit (50) to be a stiffness that makes the insertion section (40) substantially straight when the advance and retreat detection unit (50) has detected a retreat of the insertion section (40).
