A process for manufacturing a wiring substrate, comprising: a step of forming an insulating resin layer containing an inorganic filler over a wiring layer formed on at least one surface of an insulating substrate; a step of forming a thin copper film layer by roughening a surface of the insulating resin layer and plating the same electrolessly with copper; a step of forming an insulating film over the thin copper film layer; a step of forming plated resists profiling a pattern by exposing and developing the insulating film with the pattern; and a step of forming wiring pattern layers by an electrolytic copper plating on a surface of the insulating resin layer having the plated resists formed thereon, wherein at least one of the plated resists has a width of less than 20 μm, and -the plated resists include adjoining plated resists in which a clearance between said adjoining plated resists has a width of less than 20 μm.