An apparatus for controlling a neutron beam includes a plurality of columnar prisms 1 that are made of a material having a refractive index of less than 1 for a neutron beam, and are arranged so as to be multi-layered. The columnar prisms 1 each have an approximately right-triangle-shaped section, and are three-dimensionally multi-layered such that respective surfaces 1a, 1b, 1c of the columnar prisms are in parallel to one another. Stick-shaped members 5 are made of the above material, the stick-shaped members 5 are set in a plurality of grooves formed on a jig 6 that have the same shape, and upper surfaces of the grooves are flattened at the same time.