A light wavefront measuring apparatus (2, 2a, 42) includes a separating element (7a, 47a) for separating a flux of light which exits from an optical head (1, 31) into a first beam and a second beam, a first interference fringe display section (21, 21a) for displaying interference fringes formed from the first beam, a Dove prism (13, 53) for rotating a wavefront of the second beam around its optical axis (AX2), and a second interference fringe display section (22, 22a) for displaying interference fringes formed from the second beam which passed through it. In adjustment of the light source device, position of a collimator (5) in the optical head (1, 31) is adjusted in optical axis direction so as to approximate the interference fringe patterns displayed in the interference fringe display sections (21, 22, 21a, 22a) each other.