An optical measuring device includes a sensor which emits light flashes toward
a subject of detection with a light emitting element which is supplied with electric
power from a rechargeable battery for a certain duration at certain intervals and
receives reflected light from the subject with a light sensitive element. A subtractor
subtracts a d.c. component from a sensed signal provided by the light sensitive
element, thereby extracting a variation component. The subtractor has its output
signal amplified with an amplifier, with the output thereof being A/D-converted
with an A/D converter.
