The measuring apparatus (10) includes a housing (100), a translucent member (110), a light emitting unit (120), and a light detecting unit (140). An opening (102) is provided in the housing (100). The translucent member (110) is located in the opening (102) and transmits the light of the first wavelength. The light emitting part (120) and the light detecting part (140) are arranged inside the housing (100). The light emitting portion (120) radiates light including the first wavelength obliquely to the light transmitting member (110) against the outer surface of the light transmitting member (110). The light detection unit (140) is disposed in such a direction that the optical axis passes through the light transmitting member (110), and measures the intensity of the light of the first wavelength. The optical axis of the light emitting portion (120) and the optical axis of the light detecting portion (140) intersect with each other outside the light transmitting member (110), and the distance d (d) between the intersection and the outer surface of the light transmitting member Is 2 mm or less.測定装置(10)は、筐体(100)、透光部材(110)、発光部(120)、及び光検出部(140)を備えている。筐体(100)には開口(102)が設けられている。透光部材(110)は開口(102)に位置しており、第1波長の光を透過する。発光部(120)及び光検出部(140)は筐体(100)の内部に配置されている。発光部(120)は、第1波長を含む光を、透光部材(110)に、透光部材(110)の外面に対して斜めに放射する。光検出部(140)は、光軸が透光部材(110)を通る向きに配置され、第1波長の光の強度を測定する。そして、発光部(120)の光軸と光検出部(140)の光軸は、透光部材(110)の外部で交わり、かつこの交点αと、透光部材(110)の外面の距離dは、2mm以下である。
