An optical sensor includes: a light emitting element 40; a lower substrate 20 on which the light emitting element 40 is provided; an upper substrate 10 provided so that the light emitting element 40 is positioned between the upper substrate 10 and the lower substrate 20; and an optical block 30 provided on the upper substrate 10. The upper substrate 10 includes a division-type photodiode SD. The optical block 30 is configured to reflect light emitted from the light emitting element 40 toward a measurement target R, and light reflected by the measurement target R is incident onto the division-type photodiode SD.