To provide a confocal microscope for obtaining an extended image by easily determining the capturing range of an observation image without being aware of the shape of a sample to be observed, the confocal microscope comprises confocal image generating unit for generating a confocal image, first counting unit for counting a first number of pixels having a predetermined brightness level or lower among the brightness levels of the pixels of the confocal image, second counting unit for counting a second number of pixels obtained by extracting only a pixel that matches a predetermined condition for the confocal image, and boundary determining unit for detecting a boundary by determining whether or not the observation surface is within the image capturing range based on the first and the second numbers of pixels.