Intermediate multilayer wiring board product, and method for manufacturing multilayer wiring board

An intermediate multilayer wiring board product includes: a stack of a plurality of resin insulating layers, a first conductor layer, and a second conductor layer. The stack includes: a product forming region comprising a plurality of product portions arranged along a major surface of the stack, each of the plurality of product portions to become a product of the multilayer wiring board; and a frame portion surrounding the product forming region. The first conductor layer is formed on at least one of the plurality of resin insulating layers within each of the plurality of product portions. The second conductor layer is formed on at least one of the plurality of resin insulating layers within the frame portion. The frame portion has a plurality of cuts penetrating the frame portion in a thickness direction thereof, the plurality of cuts being arranged at substantially equal intervals.