The present invention relates to an aberration correcting device comprising: an aberration correcting element which modulates the phase of incident light; and a position adjusting section which can move the aberration correcting element in a direction perpendicular to an optical axis of the incident light, wherein the aberration correcting element includes first and second aberration correction plates, each of which is disposed such that the phase of transmitted light beam differs with transmission position of the incident light beam with the same phase, and the aberration correcting element has a reference arrangement which is an arrangement of the first and second aberration correction plates in which the light beams transmitted through the aberration correcting element have the same phase, and assuming that a point on the first aberration correction plate crossing the optical axis is a point Oa and a point on the second aberration correction plate crossing the optical axis is a point Ob in the reference arrangement, the position adjusting section includes a mechanism which can move the first and second aberration correction plates in a direction perpendicular to the optical axis and the points Oa and Ob in opposite directions from the reference arrangement and/or a mechanism which can rotate and move the first and second aberration correction plates by the same angle in different directions from the reference arrangement with the points Oa and Ob as the center.