A light source device comprising: a light source holding member in which a plurality of light source elements are arranged into a matrix fashion at predetermined intervals; a lens array, disposed on a light shining side of the light source elements, which has (a) a plate-shaped base portion and (b) a plurality of lens portions which are (i) arranged into a matrix fashion at predetermined intervals so as to correspond to the light source elements, respectively, and (ii) formed integrally with the plate-shaped base portion; and an array holding member which is disposed between the light source holding member and the lens array to hold the lens array, the array holding member having a plurality of light passage holes arranged into a matrix fashion at predetermined intervals so as to correspond to the light source elements, wherein the lens array has a plurality of first hole portions in the plate-shaped base portion through which first fixing screw members are inserted, and the array holding member has a plurality of first threaded hole portions with which the first fixing screw members are brought into engagement in positions which correspond to the first hole portions in the lens array, the light source device being characterized in that the first fixing screw members pass through the first hole portions in the lens array and are then brought into engagement with the first threaded hole portions in the array holding member such that a flat surface on the rear side of the plate shaped base portion of the lens array abuts against a flat surface on the front side of the array holding member, the lens array and the array holding member thereby being disposed to adhere to each other, wherein said flat surface on the front side of the array holding member includes areas around and between said light passage holes, which are disposed to adhere to corresponding areas of said flat surface on the rear side of the plate shaped base portion. a light source holding member in which a plurality of light source elements are arranged into a matrix fashion at predetermined intervals; a lens array, disposed on a light shining side of the light source elements, which has (a) a plate-shaped base portion and (b) a plurality of lens portions which are (i) arranged into a matrix fashion at predetermined intervals so as to correspond to the light source elements, respectively, and (ii) formed integrally with the plate-shaped base portion; and an array holding member which is disposed between the light source holding member and the lens array to hold the lens array, the array holding member having a plurality of light passage holes arranged into a matrix fashion at predetermined intervals so as to correspond to the light source elements, wherein the lens array has a plurality of first hole portions in the plate-shaped base portion through which first fixing screw members are inserted, and the array holding member has a plurality of first threaded hole portions with which the first fixing screw members are brought into engagement in positions which correspond to the first hole portions in the lens array, the light source device being characterized in that the first fixing screw members pass through the first hole portions in the lens array and are then brought into engagement with the first threaded hole portions in the array holding member such that a flat surface on the rear side of the plate shaped base portion of the lens array abuts against a flat surface on the front side of the array holding member, the lens array and the array holding member thereby being disposed to adhere to each other, wherein said flat surface on the front side of the array holding member includes areas around and between said light passage holes, which are disposed to adhere to corresponding areas of said flat surface on the rear side of the plate shaped base portion.