The chain end distribution of a block copolymer in a two-dimensional microphase-separated structure was Studied by scanning near-field optical microscopy (SNOM). In the monolayer of poly(octadecyl methacrylate)block-poly(isobutyl methacrylate) (PODMA-b-PiBMA), the free end of the PiBMA subchain was directly observed by SNOM, and the spatial distributions of the whole block and the chain end are examined and compared with the convolution of the point spread function of the microscope and distribution function of the model structures. It was found that the chain end distribution of the block copolymer confined in two dimensions has a peak near the domain center, being concentrated in the narrower region, as compared with three-dimensional systems.