In three-dimensional measurement where circular polarized light or elliptical polarized light is projected as measurement light, correct measurement results can be obtained irrespective of the difference in intensity between primary reflected light and secondary reflected light. A three-dimensional position measurement method includes projecting, as the measurement light, circular polarized light or elliptical polarized light onto an object to be measured, photoelectrically converting reflected light from the object to obtain a first signal, allowing the reflected light from the object to enter a quarter wavelength plate, allowing reflected light that has passed through the quarter wavelength plate to enter a polarizing device attenuating secondary reflected light that is light reflected from the object twice, photoelectrically converting reflected light that has passed through the polarizing device to obtain a second signal, and removing secondary reflected light components by using a difference between the first signal and the second signal.