An endoscope shape detection system has a CPU included in a control unit. The CPU performs frequency sampling on digital data to calculate coordinates indicating the spatial positions of source coils incorporated in an insertion unit of an endoscope and of marker coils. An inserted state of the insertion unit of the endoscope is estimated based on the calculated coordinate data indicating the positions of the source coils. Display data based on which shape of the endoscope depicted is produced from the calculated coordinate data indicating the positions of the source coils, and output to a video RAM. Display data based on which marker coils are depicted is produced from the calculated coordinate data indicating the positions of the marker coils, and output to the video RAM. Consequently, the positions of the markers are depicted together with the shape of the endoscope. The positional relationship between the insertion unit of the endoscope and a patient's body can therefore be ascertained.