To provide a foamed synthetic resin board used for a construction of a house and the like, with which subsidiary works coming up afterwards can be carried out easily and also which is excellent in strength.

The foamed synthetic resin board 1 is molded in a plate by mixing polyurethane resin material in the presence of a catalyst to make foaming-reaction. Protrusions 1b to 1g, projecting from the board surface at arbitrary positions on the foamed synthetic resin board 1. A core material 2 to form a core may be provided in the respective protrusions 1b to 1g.