A line sensor unit includes: a first light source configured to emit excitation light that excites a fluorescent substance; a second light source configured to emit non-excitation light that does not excite the fluorescent substance; a line sensor configured to receive light from a medium obtained by irradiating the medium with the excitation light or the non-excitation light; a light-emitting unit, which is excited upon receipt of the excitation light, configured to emit light responsive to the excitation light, the emitted light being incident on the line sensor; and a light-shielding unit, which is provided on a side opposite to a line-sensor side of the light-emitting unit, configured to block light advancing from the light-emitting unit to the medium.