A printed board includes a printed board body and throwaway boards provided on opposite sides of the printed board body through joining portions spaced away from each other in a longitudinal direction. Bores are provided in areas bridging the joining portions and throwaway boards. The bores can receive guide pins on a conveying unit for carrying the printed board to an electronic element mounting apparatus. The joining portions and throwaway boards can be removed from the printed board body after mounting the electronic elements on the printed board. This structure can minimize a width of a throwaway board and reduce total costs without lowering mounting efficiency of electronic elements in an electronic element mounting step.