A flexible tube insertion device according to one embodiment of the present invention includes: a tubular insertion portion which has a distal bending portion and a flexible tube portion provided on a base end side of the bending portion, and which is inserted inside a subject multiple variable rigidity portions each being provided on individual multiple segments of the flexible tube portion taken in a longitudinal axis direction and which change the flexural rigidity of the flexible tube portion in segment units a variable rigidity control unit which controls changes in the flexural rigidity of the flexible tube portion by the variable rigidity portions an imaging unit which is provided on the bending portion and images the forward direction of the bending portion and a cavity detection unit which detects the presence of cavities in the forward direction of the bending portion on the basis of an image obtained by imaging performed by the imaging unit. When the cavity detection unit detects the presence of a cavity in the substantially forward direction, the variable rigidity control unit controls at least one variable rigidity portion such that at least one of the variable rigidity portions changes the flexural rigidity of the flexible tube portion.Un dispositif dinsertion de tube flexible selon un mode de réalisation de la présente invention comprend : une partie dinsertion tubulaire qui comporte une partie de flexion distale et une partie de tube flexible disposée sur une côté dextrémité de base de la partie de flexion, et qui est insérée à lintérieur dun sujet des parties à rigidité variable multiples, chacune étant disposée sur des segments individuels multiples de la partie de tube flexible prise dans la direction de laxe longitudinal et qui modifient la rigidité à la flexion de la partie de tube flexible dans des unités de segment une unité de commande de rigidité variable qui commande des changements de rigidité à la flexion de la partie de tube flexible p
