A superimposed grating comprising a diffraction grating and a high-frequency grating, whose aim is to achieve alignment-free and multifunctional integrated optical elements, is demonstrated for the first time. Then a lightweight and compact magneto-optical disk head that uses this superimposed grating is proposed. The superimposed grating, which simultaneously operates a polarizing beamsplitter and an off-axis cylindrical lens, has three functions required for optical heads: focusing error detection, tracking error detection, and signal detection. Measured focusing and polarizing characteristics suggest that the superimposed grating has the desirable error detection and signal detection for magneto-optical disk heads. A detailed investigation of this grating with an emphasis on clarifying both its basic principles and its use with magneto-optical disk heads is presented.