To recognize the position of an endoscope inserted in a tubular tissue of a subject within the tubular tissue.

The center line L of a tubular tissue of a subject is acquired from a previously acquired three-dimensional image of the subject, an endoscopic image captured while moving the endoscope inserted in the tubular tissue along the longitudinal direction of the tubular tissue is displayed. When one feature region of the tubular tissue is displayed in the displayed endoscopic image, the reference position of the endoscope is input and a position Q1 corresponding to the one feature region is set on the center line L. The amount of movement and the direction of travel of the endoscope moved further from the reference position are acquired, the position distant by the acquired amount of movement in the acquired direction of travel along the center line from the position Q1 corresponding to the one feature region is calculated as a present position Q2, and an indicator M indicating the calculated present position Q2 is displayed on the center line L.