An optical pulse time spreader which can generate a chip pulse string of which intensity is equalized. The reflectances R.sub.1, R.sub.2 and R.sub.k of the first, second and k-th (k is an integer which satisfies 3.ltoreq.k.ltoreq.J) unit FBG are given by the following formulae respectively. R.sub.1=P.sub.c(constant) (a) R.sub.2=P.sub.c/(1-R.sub.1).sup.2 (b) R.sub.k=(P.sub.c.sup.1/2-P.sub.k.sup.1/2).sup.2/{(1-R.sub.1).sup.2(1-R.su- b.2).sup.2 . . . (1-R.sub.k-1).sup.2} (c-1) R.sub.k=(P.sub.c.sup.1/2+P.sub.k.sup.1/2).sup.2/{(1-R.sub.1).sup.2 (1-R.sub.2).sup.2 . . . (1-R.sub.k-1).sup.2} (c-2)Here P.sub.c is an arbitrary constant, and P.sub.k is an intensity of a triple reflection chip pulse which is output for the k-th time. The formulae (c-1) and (c-2) are the reflectance of the k-th unit diffraction grating when the phase difference between the single reflection chip pulse, which is output for the k-th time, and the triple reflection chip pulse, which is output for the k-th time, is 0 and .pi. respectively.