An embodiment of the present invention is a flexible tube insertion device having a flexible insertion part inserted in a subject. The flexible tube insertion device is provided with: an insertion part state detection part for detecting a state of the insertion part necessary for estimating insertion when the insertion part is inserted in the subject an insertion estimation part for estimating, using information of a detection state detected by the insertion part state detection part, an advancement state of a distal end of the insertion part and a state of the subject when the insertion part is pushed in further from the detection state and an output part for performing output on the basis of the estimation obtained from the insertion estimation part.
