An optical module, comprising: a circuit board mounting an optical element array thereon; a resin molded body disposed on the circuit board; and a prism/lens array having lenses lined in its width direction, which can reflect light and is glass-made; wherein, the resin molded body has a prism-securing part which is provided on a part aligned with the optical element array and adapted to fix the prism/lens array therein and part of which is an opening penetrating opposing surfaces of the resin molded body for inserting the prism/lens array, an opening part provided in the prism-securing part and formed toward an optical connector connected thereto, and a guiding part for positioning of the optical connector; a fitting structure for positioning the prism/lens array in its width direction is formed on the contact surfaces between the prism/lens array and the prism-securing part, such that the prism/lens array can be positioned in its front-back direction and height direction by contact between the prism/lens array and the prism-securing part; wherein the fitting structure comprises one of a pair of protrusions or a pair of grooves formed on the surface of the prism/lens array in contact with with the prism securing part each one of the pair being on either side of the lenses on the lens surface facing the optical array, and the other one of the pair of protrusions or the pair of grooves formed on the surface of the prism-securing part contacting the prism/lens array and positioned such that the pair of protrusions and the pair of grooves can fit into each other; wherein the pair of grooves are respectively formed along the inserting direction of the prism/lens array, such that the prism/lens array can be positioned in its width direction by surface contact between the respective protrusions and grooves. a circuit board mounting an optical element array thereon; a resin molded body disposed on the circuit board; and a prism/lens array having lenses lined in its width direction, which can reflect light and is glass-made; wherein, the resin molded body has a prism-securing part which is provided on a part aligned with the optical element array and adapted to fix the prism/lens array therein and part of which is an opening penetrating opposing surfaces of the resin molded body for inserting the prism/lens array, an opening part provided in the prism-securing part and formed toward an optical connector connected thereto, and a guiding part for positioning of the optical connector; a fitting structure for positioning the prism/lens array in its width direction is formed on the contact surfaces between the prism/lens array and the prism-securing part, such that the prism/lens array can be positioned in its front-back direction and height direction by contact between the prism/lens array and the prism-securing part; wherein the fitting structure comprises one of a pair of protrusions or a pair of grooves formed on the surface of the prism/lens array in contact with with the prism securing part each one of the pair being on either side of the lenses on the lens surface facing the optical array, and the other one of the pair of protrusions or the pair of grooves formed on the surface of the prism-securing part contacting the prism/lens array and positioned such that the pair of protrusions and the pair of grooves can fit into each other; one of a pair of protrusions or a pair of grooves formed on the surface of the prism/lens array in contact with with the prism securing part each one of the pair being on either side of the lenses on the lens surface facing the optical array, and the other one of the pair of protrusions or the pair of grooves formed on the surface of the prism-securing part contacting the prism/lens array and positioned such that the pair of protrusions and the pair of grooves can fit into each other; wherein the pair of grooves are respectively formed along the inserting direction of the prism/lens array, such that the prism/lens array can be positioned in its width direction by surface contact between the respective protrusions and grooves.