A super structure fiber Bragg grating is produced without being limited by a phase mask length. First, a beam is allowed to scan with the relative position between a mask and an optical fiber fixed (step 1). Subsequently, the relative position between the mask and the optical fiber is moved in the lengthwise direction of the optical fiber (step 2). Besides, the beam is allowed to scan with the relative position between the mask and the optical fiber fixed as at the step 1. Next, in order to correct and match a phase deviation, the mask is removed, and a uniform ultraviolet beam is applied to the optical fiber, whereby a refractive index can be uniformly changed, and the optical length of the corresponding portion is changed to impart a phase shift (step 3). The phase shift-imparting position may be the place between both the fixed positions or any other suitable place. A phase shift amount is determined by an ultraviolet beam irradiation time (or light pulse number), and if a necessary phase shift amount has been attained is determined while a reflection spectrum is being observed. The SSFBG of free length can be fabricated by repeating the above steps.