A Raman scattered light acquisition device , comprising: an emission optical system which is configured to guide excitation light from a light emission unit into a fluid (G) along an optical axis (Aw); a scattered light window which is configured to define a part of a flow path of the fluid (G) and through which Raman scattered light from the fluid (G) irradiated with the excitation light passes; a scattered light receiving device which has a light receiving surface receiving the Raman scattered light which has passed through the scattered light window ; wherein the scattered light window and the light receiving surface of the scattered light receiving device are arranged at positions in which the scattered light window and the light receiving surface are separated from the optical axis (Aw) in the fluid (G) in a radial direction (Dr) which is a direction perpendicular to the optical axis (Aw) in the fluid (G) within a range in which an optical path of the excitation light in the fluid (G) is present in an optical axis direction (Da) in which the optical axis (Aw) in the fluid (G) which is the optical axis of the excitation light in the fluid (G) extends, the light receiving surface faces a radially inward side (Dri) which is a side in proximity to the optical axis (Aw) in the fluid (G) in the radial direction (Dr), characterized in that the Raman scattered light acquisition device further comprises a light shielding member through which the excitation light and the Raman scattered light do not pass, wherein the light shielding member is in contact with an outer surface of the scattered light window on the light receiving surface side, a heating optical fiber cable arranged to irradiate the light shielding member with heating laser light; a cavity which extends along the outer surface of the scattered light window is formed inside the light shielding member , wherein the heating optical fiber cable is configured to emit into the cavity of the light shielding member . an emission optical system which is configured to guide excitation light from a light emission unit into a fluid (G) along an optical axis (Aw); a scattered light window which is configured to define a part of a flow path of the fluid (G) and through which Raman scattered light from the fluid (G) irradiated with the excitation light passes; a scattered light receiving device which has a light receiving surface receiving the Raman scattered light which has passed through the scattered light window ; wherein the scattered light window and the light receiving surface of the scattered light receiving device are arranged at positions in which the scattered light window and the light receiving surface are separated from the optical axis (Aw) in the fluid (G) in a radial direction (Dr) which is a direction perpendicular to the optical axis (Aw) in the fluid (G) within a range in which an optical path of the excitation light in the fluid (G) is present in an optical axis direction (Da) in which the optical axis (Aw) in the fluid (G) which is the optical axis of the excitation light in the fluid (G) extends, the light receiving surface faces a radially inward side (Dri) which is a side in proximity to the optical axis (Aw) in the fluid (G) in the radial direction (Dr), characterized in that the Raman scattered light acquisition device further comprises a light shielding member through which the excitation light and the Raman scattered light do not pass, wherein the light shielding member is in contact with an outer surface of the scattered light window on the light receiving surface side, a heating optical fiber cable arranged to irradiate the light shielding member with heating laser light; a cavity which extends along the outer surface of the scattered light window is formed inside the light shielding member , wherein the heating optical fiber cable is configured to emit into the cavity of the light shielding member . <EOS>