There is provided an optical pickup device comprising a laser light source for emitting a laser beam, an object lens for focusing the laser beam onto the recording surfaces of layers 0 and 1 of an optical disk and condensing the laser beam onto the recording surfaces, photodetectors for receiving the laser beam reflected by the optical disk, and a diffraction grating for diffracting a part of the reflected laser beam toward the photodetectors, wherein data can be simultaneously written to layers 0 and 1. The photodetector detects the reflected light from layer 0 after being refracted by the diffraction grating, and detects the reflected light from layer 1 without being refracted, so that the data of layers 0 and 1 can be simultaneously read. Thus, data can be simultaneously read from and written to the recording surfaces of a plurality of layers of an optical disk.