A multi-mode optical coupler which includes an integrated section in which two optical fibers are fused and integrated together, at least one of these optical fibers being a multi-mode fiber, the multi-mode optical coupler coupling multi-mode light carried in the one of the multi-mode fibers to the other of the optical fibers, wherein: assuming that an outline of the integrated section in a plane view of the optical coupler is a function of a position along the longitudinal direction of the fibers, the multi-mode optical coupler has a plurality of inflection points along the outline; the multi-mode optical coupler satisfies: in an area between the farthermost inflection points includes: the length of the area between the inflection points is not more than 2 mm and an outer diameter h2 of the optical fibers along the direction in which the optical fibers are arranged in parallel is in the range of 70% to 80% of a sum of the outer diameters of the optical fibers; or the length of the area between the inflection points is not less than 1 mm and not more than 2 mm and the outer diameter h2 is in the ranges of 50% to 70% and 80% to 90% of the sum of the outer diameters of the optical fibers.