Abstract: An automatic focusing device for controlling the position of the objective lens relative to the information recording medium is provided with an astigmatic optical system which receives the reflected light beam reflected by the information recording medium. The light receiving surface of a light detector included in the astigmatic optical system consists of a central light receiving section formed approximatley symmetrically with respect to two axes intersecting each other perpendicularly and having a constricted central portion, and two side light receiving sections formed approximately symmetrically with respect to those two axes and opposite to each other. The light reception signal given by the central light receiving section and the light reception signals given by the side light receiving sections are fed to a focal position detecting circuit which gives a signal corresponding to the deviation of the objective lens from the focused position, on the basis of the light reception signals given thereto.