A method is proposed for accurately measuring a sectional profile of a metal cylinder. In this method a sinusoidally vibrating sinusoidal interference pattern is used to generate an exact spatial scale along one direction. Light from top points of a metal cylinder surface is extracted by spatial filtering in an afocal imaging system to form an image of the top points. A time-varying signal is detected in the image, and a sectional profile of the metal cylinder is measured from the phase of the detected signal on a position where the amplitude of the signal has a maximum value. Detection of the amplitude and the phase is carried out easily and exactly with sinusoidal phase-modulating interferometry. (c) 2006 Society of Photo-Optical Instrumentation Engineers.