A flexible tube insertion apparatus (10) includes an insertion section (40), and a detection unit (60) that detects state information of the insertion section (40) . The flexible tube insertion apparatus (10) includes an insertability determination portion (121) that determines whether an insertability of the insertion section (40) into a deep portion from a current position is decreased or not, and a stiffness change range decision portion (127) that, when the insertability determination portion (121) determines that the insertability of the insertion section is decreased, decides a stiffness change range (411) in a part of the insertion section (40) used for determination of the insertability determination portion (121). The flexible tube insertion apparatus (10) includes a stiffness control portion (129) that controls a bending stiffness of the insertion section (40) in the stiffness change range (411) decided by the stiffness change range decision portion (127), so as to be a bending stiffness that makes the insertion section (40) substantially straight in the stiffness change range (411).
