To provide a speckle interferometry system of a two-flux illuminating direction switchable type, which simultaneously and precisely carry out respective phase shift operations about illuminations of two fluxes in directions different from each other.

An optical path length adjustable means 60 is disposed at an optical member mount section 10. The optical path length adjustable means 60 is configured such that two phase shift operations are carried out simultaneously in a centralized fashion, wherein optical path length differences between one side illuminating fluxes 14b, 15a which pass through a reflection optical element 61, and the other side illuminating fluxes 14a, 15b which do not pass through the reflection optical element 61, are varied by using one drive means 62 which moves the optical element 61 minutely.