COMPOUND OBJECTIVE LENS, DIFFRACTION ELEMENT, OPTICAL HEAD DEVICE, OPTICAL INFORMATION DEVICE, OBJECTIVE LENS DRIVING METHOD AND CONTROL DEVICE

PROBLEM TO BE SOLVED: To provide an optical head device for using an objective lens having a large NA to record or playback a high-density optical disk, in which a sawtooth-shaped diffraction element is used to record and playback a conventional optical disk, such as a DVD and a CD.SOLUTION: In one embodiment of a compound objective lens such as in an optical head device, a level difference in which optical path length is one wavelength or more for blue light, and optical path length is less than one wavelength for red light and infrared light is used to give an action reverse to the red light and the infrared light to the blue light. By an effect of making working distance to a CD and a DVD large, compatibility between the CD and the DVD can be achieved. An optical element is formed with an objective lens into a signal body to perform tracking servo tracking.