A sensor unit for measuring a response characteristic of a polarization rotation liquid crystal cell, includes a measurement light source which emits measurement light, a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to a polarization rotation liquid crystal cell, a second polarization plate which has a second polarization direction and receives measurement light passed through the polarization rotation liquid crystal cell, a light receiving unit which receives measurement light passed through the second polarization plate, and a measurement unit which determines a response characteristic of the polarization rotation liquid crystal cell on the basis of a drive signal of the polarization rotation liquid crystal cell and the amount of measurement light received by the light receiving unit.