To widen the usable range of a spectrum sonde by incorporating a small-sized UV lamp containing a continuous body in the ultraviolet spectrum region in a light source used for illuminating a material to be measured.

A spectrophotometer has a full length of about 15 cm and a diameter of about 5 cm and is provided with a small-sized heavy hydrogen lamp 2, a detector 3, a microprocessor 4, a battery 5, etc., housed in a resin case 1. The case 1 has a light-emitting window 7 composed of quartz glass in its front end section, and a sample 8 to be measured is placed in front of the window 7. The ultraviolet beam emitted from the lamp 2 is introduced to the window 7 and sample 8 through an optical waveguide 9, and the reflected beam of the ultraviolet beam from the sample 8 reaches the detector 3 through a second optical waveguide 10. The detector 3 converts the optical signal into an electric pulse, and the pulse is evaluated by and stored in the microprocessor 4 and read out to an external computer. The lamp 2 has divided discharging sections and is operated through the battery 5, and a high frequency generator 11 and the spectrum of the lamp 2 has a continuous body in the wavelength region of about 200-350 μm.