In a photoelectric conversion apparatus obtained by arranging and fixing a plurality of semiconductor element substrates onto a base with an adhesive, the levels of the upper surfaces of the substrates are adjusted with a desired thickness of the adhesive so as to set the upper surfaces within the same plane while the distance from the upper surface of the base to the semiconductor element surface of each substrate is kept to a design value, thereby realizing a photoelectric conversion apparatus constituted by a plurality of substrates arranged two-dimensionally, which eliminates level gaps between the substrates, and hence is free from problems such as a decrease in resolution, a deterioration in sensitivity, and peeling of a phosphor and the like.