An occurrence of a noise in a light receiver is suppressed, and an accuracy of measuring a film thickness is improved. A film thickness measuring apparatus includes: a stage being in contact with only an end portion of a substrate; a reflection suppressing unit located separately from the stage in a region surrounded by the stage; a light source; and a light receiver which a first light made up of light, which has been emitted from the light source, reflected on an upper surface of the measured film and a second light reflected on an upper surface of the substrate enter. The reflection suppressing unit is located separately from a lower surface of the substrate exposed to atmosphere, and suppresses a reflection of light, which enters the reflection suppressing unit from the light source, to the light receiver.