Pattern inspection method, photomask inspection device, and photomask manufacturing method

The invention provides a pattern inspection method, a photomask inspection device, and a photomask manufacturing method. Even in a fine width pattern, line width measurement can be performed stably and with high precision. The pattern inspection method comprises: a step for irradiating an inspection region with light and acquiring a transmitted light image of the inspection region; a step for obtaining light intensity distribution data of the inspection region on the basis of the acquired transmitted light image; a differential processing step of obtaining a light intensity change curve of a region including a first boundary, which is a boundary portion between a first transmission control unit and a second transmission control unit, and a second boundary, which is a boundary portion between the second transmission control unit and a third transmission control unit, by performing differential processing on a light intensity distribution curve obtained from the light intensity distribution data; a fitting step