A substrate on which a plurality of semiconductor light-emitting elements are to be linearly mounted to form an element row, the substrate comprising: a first line and a second line which are disposed such that the element row is interposed therebetween, wherein the first line includes a first main line portion extending mainly in a row direction of the element row, and a plurality of first connecting portions connected to the first main line portion and for connecting to a corresponding one of the semiconductor light-emitting elements, and the second line includes a second main line portion extending mainly in the row direction of the element row, and a plurality of second connecting portions connected to the second main line portion and for connecting to a corresponding one of the semiconductor light-emitting elements, wherein each of the plurality of first connecting portions of the first line includes a protruding portion which protrudes toward the second line, and each of the plurality of the second connecting portions of the second line includes a protruding portion which protrudes toward the first line, characterized in that respective pairs of connecting portions composed of one of the first connecting portions and one of the a second connecting portions are arranged to be connected to one light-emitting element of the light-emitting elements to be provided between said one first connecting portion and said one second connecting portion of the respective pair by wire bonding said one first connecting portion to said one light-emitting element and wire bonding said one second connecting portion to said one light-emitting element; an outline of the first main line portion is formed to curve on the side facing the second line and an outline of the second main line portion is formed to curve on the side facing the first line so that the first main line portion and the second main line portion have a line width which is broader at their ends than at the center in the row direction; due to the curved sides of the first main line portion and the second main line portion, a gap between a first main line portion and the second main line portion is larger at element mounting positions at which the semiconductor light-emitting elements are to be mounted than at positions other than the element mounting positions. a first line and a second line which are disposed such that the element row is interposed therebetween, wherein the first line includes a first main line portion extending mainly in a row direction of the element row, and a plurality of first connecting portions connected to the first main line portion and for connecting to a corresponding one of the semiconductor light-emitting elements, and the second line includes a second main line portion extending mainly in the row direction of the element row, and a plurality of second connecting portions connected to the second main line portion and for connecting to a corresponding one of the semiconductor light-emitting elements, wherein each of the plurality of first connecting portions of the first line includes a protruding portion which protrudes toward the second line, and each of the plurality of the second connecting portions of the second line includes a protruding portion which protrudes toward the first line, characterized in that respective pairs of connecting portions composed of one of the first connecting portions and one of the a second connecting portions are arranged to be connected to one light-emitting element of the light-emitting elements to be provided between said one first connecting portion and said one second connecting portion of the respective pair by wire bonding said one first connecting portion to said one light-emitting element and wire bonding said one second connecting portion to said one light-emitting element; an outline of the first main line portion is formed to curve on the side facing the second line and an outline of the second main line portion is formed to curve on the side facing the first line so that the first main line portion and the second main line portion have a line width which is broader at their ends than at the center in the row direction; due to the curved sides of the first main line portion and the second main line portion, a gap between a first main line portion and the second main line portion is larger at element mounting positions at which the semiconductor light-emitting elements are to be mounted than at positions other than the element mounting positions.