light whose frequency difference is controlled and irradiates a measurement object 6 with measuring light via the light probe 3 the scattered light produced by the measurement object scattering the measuring light is integrated with the locally oscillated light via the light probe 3 and is directed to the optical heterodyne detector 2 the control computer 4 finds the center frequency and linewidth of the brillouin scattered components by analyzing the spectrum of the scattered light the center frequency of the brillouin scattered components depends on elasticity and the linewidth depends on viscosity and information about the elasticity and viscosity in the target area can therefore be obtained from this measurement the control computer 4 formulates as image information the information about elasticity and or viscosity obtained by the spectrum analysis and outputs this information to the image information display device 5 the light source 1 outputs two beams of light from separate ports one for measuring light having frequency f 1 and one for locally oscillated light having frequency f 2 the measuring light is emitted by a laser light source 101 and the locally oscillated light is emitted by a variable frequency laser light source 102 the measuring light and the locally oscillated light are integrated and are photoelectrically converted by a photodiode 103 an electric signal is inputted to a frequency measuring instrument 104 to measure the difference in frequency between the measuring light and the locally oscillated light an error signal indicating an error between the measured value and the value designated by the control computer 4 is created by a frequency control circuit 105 and feedback is supplied to the variable frequency laser light source 102 this light source reduces noise because the.