To provide a level difference position detection device and a total width/level difference position detection apparatus which can precisely detect, for a sheet body, the width and the position of a level difference part existing on the major surface.

A seal position measuring device 1 is composed of rolls 11 and 12 whose central axes are disposed parallel to each other, CCD line sensors 13a and 14a, a photoelectric sensor 15a, a stepping motor 17 for driving the photoelectric sensor 15a in the y-direction, a data processing part 18 for performing the data processing and for controlling the stepping motor 17, and so forth. A resin film 5 abuts against the surface of the lower roll 12 in the state in which the tension is applied, in which the major surface that is opposite the surface on which the level difference part exists is brought into close contact with the surface of the lower roll 12 so that the posture thereof is corrected. The sensors 13a, 14a, and 15a and light sources 13b, 14b, and 15b are set so that the optical path is perpendicular to the y-z plane.