A multilayer printed wiring board (11) is composed of a plurality of printed wiring boards (21a and 21b) each having wiring on its both sides, and a relaxing connection layer (15) for interconnecting the printed wiring boards (21a and 21b). The relaxing connection layer (15) contains an inorganic filler, a thermosetting resin, and a reliever for relieving internal stress. The multilayer printed wiring board (11) is prevented from warpage by making the relaxing connection layer (15) disposed inside it absorb internal stress caused by heating and cooling in a solder reflow process or other processes.