PURPOSE: To improve a scanning characteristic and a convergency by adding a specific correction term to a spatial frequency so that an image-forming position in the focus of a zone plate can be made into the product of the focusing distance and the scanning angle of an incident light.

CONSTITUTION: A correction term proportionate to the n-th power [(n) is a positive real number] of the distance from an optical axis of the zone plate is added to the spatial frequency so that the image-forming position in the focusing surface of the zone plate can be made into the product of a focusing distance (f) and a scanning angle θ of the incident light. A cosine wave type phase change on the zone plate specified by the space frequency is binarized and made into an amplitude hologram or a phase hologram. Such a calculation can be easily executed at high speed by a computer. When the amplitude type hologram or phase type hologram is prepared by using an interference fringe to be binarized in such a way, a holographic fθ lens can be obtained. Thus, the scanning characteristic and convergency can be improved.