A wiring board includes an insulating substrate composed of a stack of a plurality of insulating layers, the insulating substrate having an upper face, a lower face, and side faces; and a plurality of line conductors formed of platinum or a metallic material comprising platinum as a main component, the plurality of line conductors each including a first end and a second end located on a side opposite to the first end, the plurality of line conductors being respectively disposed in interlayers between the plurality of insulating layers, in the line conductors, a line width of a line conductor located in an interlayer among the interlayers which interlayer is closest to the upper face or the lower face of the insulating substrate being greater than a line width of a line conductor located in each of the other interlayers.