1. An endoscope, comprising: an imaging element disposed at a distal end of the endoscope that obtains images through a stereo optical adapter; a template image extracting unit comprising hardware that extracts a template image from blade images obtained by the imaging element by capturing blades periodically arrayed in a jet engine; an image comparing unit comprising hardware that compares the template image with the blade images; an image selecting unit comprising hardware that selects an image from the blade images based on a result of the image comparison of the image comparing unit; a first difference extracting unit comprising hardware that extracts a plurality of differences between the template image and the image selected by the image selecting unit; a measurement unit comprising hardware that executes measurement based on an image corresponding to the position of one of the plurality of differences extracted by the first difference extracting unit; and an input unit comprising hardware to which an instruction by a user to select one of the plurality of differences extracted by the first difference extracting unit is input; wherein the measurement unit executes, based on an image corresponding to the position of the difference indicated by the instruction input by the user to the input unit, stereo measurement using environmental data for correcting optical distortion of the stereo optical adapter to display a result of the measurement based on the environmental data.