To provide a wiring board wherein a stress applied to a board around a joint part between a product board and a waste board is eliminated when the joint part is split by a cutting line after component mounting and an adverse effect on the part mounting part is prevented.

A wiring board 10 of four-layer structure comprising boards 10a to 10d has a structure wherein a product board 16 is split from a waste board 14 by a cutting line 18 and they are connected with each other by a joint 12, and the boards 10a and 10d as an outermost layer on front and rear surfaces are removed in the joint 12 as shown in diagram 2 (B) and only the boards 10b and 10c as an inner layer work as a joint, so that the joint 12 is made smaller in thickness than the product and waste boards 16 and 14. Therefore, the bending strength of the joint 12 is smaller than the boards 14 and 16. When it is cut for splitting, there is no fear of application of mechanical stress to the product board 16 adjacent to the joint 12.