In the field of biology and medicine, observation object of the microscope has been changing from the thin specimen
to the thick living tissue. Furthermore, observation of the internal structure of a living tissue is also desired by low
invasion. However, the real structure of a phase object with three-dimensional distribution such as a living tissue is
difficult to observe, because of the influence of the phase distribution before and behind of observation position. We
enabled observation of the internal structure of living tissue without stain, by adding a new function to reduce the
influence of phase distribution to our Retardation-Modulated differential interference contrast (RM-DIC) microscope
system.