The invention comprises FBG sensor sections 3 disposed in an insertion portion 12 to be inserted into the interior of an examinee 11 provided with a plurality of FBG sensor sections 3A that detect distortion of the insertion portion 12, a coordinate calculation section 9C that calculates first three-dimensional coordinates of the respective FBG sensor sections 3 according to a first three-dimensional coordinate system whose origin is a predetermined position based on the detection results of the FBG sensor sections 3, a coordinate system setting section 9D that sets a second three-dimensional coordinate system based on the first three-dimensional coordinates of the respective FBG sensor sections 3, a coordinate transformation section 9E that transforms the first three-dimensional coordinates of the respective FBG sensor sections 3 into second three-dimensional coordinates according to the second three-dimensional coordinate system set by the coordinate system setting section 9D and shape calculation means 9F that calculates the shape of the insertion portion 12 based on the second three-dimensional coordinates transformed by the coordinate transformation section 9E.
