The self-mixing effect of a microchip laser is applicable to optical CT (Computed Tomography) because of high sensitivity to weak light of the effect. Two acousto-optic modulators were used to frequency-shift the output beam from a microchip laser by several megahertz. The beam was attenuated by passing it through a scattering object and then re-injected into the microchip laser's cavity. The self-mixing effect modulated the output intensity of the laser at a frequency of several megahertz, and the intensity of modulation was measured by a spectrum analyzer. With a ring-type optical path, which is considered to be adequate for optical CT because the light only passes through the object once, it was possible to detect a beam attenuated by more than -90 dB by neutral density filters (ND filters), and to detect a beam attenuated by INTRALIPID-10 percent solution with a concentration of 28 percent, which has the same scattering-absorption characteristic as biological tissue. By Adjusting the frequency-shift towards the relaxation-oscillation frequency of the microchip laser increased the thickness of INTRALIPID-10 percent through which transmission was possible by a factor of two. Imaging through a scattering object by using this method was demonstrated.