A method for manufacturing a detection device includes the steps of providing bonding bumps on at least one of a light-receiving element array and a read-out circuit multiplexer, fixing a bump height adjusting member for adjusting the heights of the bumps to the light-receiving element array and/or the read-out circuit multiplexer on which the bumps are provided, and pressing a flat plate on the tops of the bumps and deforming the bumps until the flat plate comes in contact with the end of the bump height adjusting member.