Using an LED element as a light source, a photometric unit including the light source, a light receiving element and other components therebetween is reduced in size. A holder 30 detachable from the device as a unit holds a light emission unit 15 formed of an LED and a light receiving element 21, and the holder is placed inside a thermostatic chamber 18 which holds a constant temperature fluid 17. Thus, the photometric unit is reduced in size.