a light emitting section for emitting a first laser beam having wavelength λ1 and a second laser beam having wavelength λ2 different from the wavelength λ1;

a surface relief type first diffraction grating having a phase height of two steps produced by being equipped with a first phase grating and a second phase grating arranged at opposite sides of the first phase grating and adapted to split the laser beam of the wavelength λ1 into three beams and transmit substantially all of the laser beam of the wavelength λ2;

a surface relief type second diffraction grating having a phase height of two steps produced by being equipped with a first phase grating and a second phase grating arranged at opposite sides of the first phase grating and adapted to split the laser beam of the wavelength λ2 into three beams and transmit substantially all of the laser beam of the wavelength λ1;

an objective lens for converging the laser beams emitted from the light emitting section onto an optical disc;

an optical element for branching optical paths of return light reflected by the optical disc; and

a light receiving section for receiving the return light branched by the optical element, wherein the light emitting section emits a second laser beam having a wavelength λ2 of about 785 nm, and the second diffraction grating includes a first phase grating having a width W1 and a second phase grating arranged at opposite sides of the first phase grating and having a width W2, the widths satisfying a relationship of 0.67×P<(W1+2×W2)<0.89×P, where P being the pitch of the diffraction grating, the first phase grating and the second phase grating having respective phase heights not smaller than 0.93 times and not greater than 1.06 times of λ2/(N2−1) and not smaller than 0.74 times and not greater than 1.06 times of λ2/(N2−1), where N2 being the refractive index for the laser beam of the wavelength of λ2 entering the diffraction grating.