In an automatic optical measurement method according to the invention, with a
movable reflection plate 6 moved to place under an optical axis, light projected
from a light projecting portion 3a is received by a light receiving
portion 3b via the movable reflection plate 6, a stationary
reflection plate 11 and the movable reflection plate 6, whereas with
the movable reflection plate 6 moved away from the optical axis and a reference
8 set on a sample stage 10, light projected from the light projecting
portion 3a is received by the light receiving portion 3b
via the reference 8 whereby a ratio between the intensities of the received
lights is determined. During a sample measurement, light projected from the light
projecting portion 3a with the movable reflection plate 6 moved
to place under the optical axis is received by the light receiving portion 3b
via the movable reflection plate 6, stationary reflection plate 11
and movable reflection plate 6 so that the intensity of light thus received
and the above ratio are used for estimating an intensity of light to be measured
with the reference, the estimated intensity of light being used for correcting
an intensity of light received via a sample.
