A housing (20) has a passage port (3) that serves as both the outlet for the illumination light (IL) to go out of the housing (20) toward a sample surface (S) and the inlet for the reflection light (RL) reflected on the sample surface (S) to enter the housing (20). A transparent member (19) is disposed at the passage port (3) to prevent dust including paper dust from entering the housing (20). A light quantity calculation unit (71) calculates the light quantity of light received by a light reception lens (33). A notification unit (81) performs a predetermined notification when the light quantity is less than or equal to a predetermined value.