Patent ID: 7891094

Claim:
A method of manufacturing a hollow body having an external surface randomly provided with a large number of depressions, comprising the steps of: providing the large number of depressions on the external surface of the hollow body; obtaining a profile curve of the external surface in a circumferential direction while rotating the hollow body; performing a frequency analysis on the obtained profile curve; and judging a quality of the hollow body by comparing a result of the frequency analysis with a predetermined judgment standard, wherein the hollow body includes thereinside a magnetic field generating device, and attracts a developer to the external surface thereof with magnetic force of the magnetic field generating device, and a peak intensity of a spectrum within a range of wavelengths not more than 1 mm, which is figured out by performing the frequency analysis using the profile curve in the circumferential direction of the external surface, is closely below a wavelength of 0.3 mm and is not more than 12 dB.