An optical-element supporting device includes a first supporting unit and a second supporting unit configured to support an optical element. The first and second supporting units are spaced apart. The first and second supporting units support the optical element so as to constrain translational motion of the optical element along each of three axial directions and rotation of the optical element about each of the three axes. Where n is the number of axes constrained by the first supporting unit among the translational motion of the optical element along each of the three axial directions and the rotation of the optical element about each of the three axes, and m is the number of axes constrained by the second supporting unit among the translational motion of the optical element along each of the three axial directions and the rotation of the optical element about each of the three axes, n+m=6 is satisfied.