A method of production of a product from a stock pulp sheet uses conveyor rolls to convey a stock pulp sheet to a crusher. During conveyance to the crusher, a defective part in the stock pulp sheet is detected by a detector. The detected defective part is removed from the stock pulp sheet by a remover. The stock pulp sheet from which the defective part is removed is supplied to the crusher to produce crushed pulp. The produced crushed pulp is used to produce a product in a product producer.