A phase-modulation-element adjustment system including: a positional-relationship adjustment unit that is used for a laser-scanning confocal observation apparatus including a plurality of image-forming lenses for forming a final image and at least one intermediate image and a wavefront-disturbing element and a wavefront-restoring element being placed at positions between which any of the intermediate images formed by the image-forming lenses is disposed and having opposite phase characteristics to each other and that is capable of adjusting a relative positional relationship between the wavefront-disturbing element and the wavefront-restoring element; a wavefront-aberration measurement unit for measuring a wavefront aberration of light that has come from an object and that has passed through the wavefront-disturbing element and the wavefront-restoring element; and a processor for controlling the positional-relationship adjustment unit so that the wavefront aberration measured by the wavefront-aberration measurement unit decreases.