A sensor hood (21) includes a bottom surface-forming section (26) that forms a flat bottom surface (26a) facing a detection space (K1). When seen from a height direction (Z1) perpendicular to a surface width direction (X1) and a surface forward/rearward direction (Y1) of the bottom surface (26a), a split section (P1) between a fixed body (30) and a split body (40) divides the bottom surface (26a) into a first range (H1) including an optical axis (CL3) in the surface width direction (X1) and a second range (H2) that avoids the optical axis (CL3). The first range (H1) is disposed at the same height as the second range (H2) in the height direction (Z1) and disposed closer to the optical axis (CL3) than the second range (H2).