1. A pattern measuring method comprising: scanning a sample with a charged particle beam to form image data based on charged particles emitted from the sample; contouring a pattern edge contained in the image data; and using an imaged contour to measure a pattern formed on the sample, wherein: the contouring includes, with respect to a band-shaped portion that is in the image data and corresponds to the pattern edge and from which the imaged contour is extracted, forming a first measured contour along positions within the band-shaped portion showing first brightness, and forming a second measured contour along positions within the band-shaped portion showing second brightness, and the measuring includes measuring a dimension between the two measured contours.