A detector module for a radiation detector in a radiation imaging apparatus is provided. The detector module includes a detecting element array including a plurality of detecting elements arranged in a matrix form in first and second directions orthogonal to each other, the detecting element array configured to allow radiation to penetrate through spaces defined between the detecting elements, an electronic circuit arranged on a radiation emission side of the detecting element array, and a radiation shielding body arranged on a radiation incident side of the detecting element array. The radiation shielding body includes a base material having radiation permeability and formed with a plurality of grooves extending in the first direction at respective positions corresponding to spaces between the detecting elements in the second direction, and a plurality of radiation shielding materials each inserted in a respective groove of the plurality of grooves.